Apo-2 ligand

ABSTRACT

A novel cytokine, designated Apo-2 ligand, which induces mammalian cell apoptosis is provided. The Apo-2 ligand is believed to be a member of the TNF cytokine family. Compositions including Apo-2 ligand chimeras, nucleic acid encoding Apo-2 ligand, and antibodies to Apo-2 ligand are also provided. Methods of using Apo-2 ligand to induce apoptosis and to treat pathological conditions such as cancer, are further provided.

FIELD OF THE INVENTION

The present invention relates generally to the identification,isolation, and recombinant production of a novel cytokine, designatedherein as “Apa-2 ligand”, which induces mammalian cell apoptosis, and tomethods of using Apo-2 ligand.

BACKGROUND OF THE INVENTION

Control of cell numbers in mammals is believed to be determined, inpart, by a balance between cell proliferation and cell death. One formof cell death, sometimes referred to as necrotic cell death, istypically characterized as a pathologic form of cell death resultingfrom some trauma or cellular injury. In contrast, there is another,“physiologic” form of cell death which usually proceeds in an orderly orcontrolled manner. This orderly or controlled form of cell death isoften referred to as “apoptosis” [see, e.g., Barr et al.,Bio/Technology, 12:487-493 (1994)]. Apoptotic cell death naturallyoccurs in many physiological processes, including embryonic developmentand clonal selection in the immune system [Itoh et al., Cell, 66:233-243(1991)]. Decreased levels of apoptotic cell death, however, have beenassociated with a variety of pathological conditions, including cancer,lupus, and herpes virus infection [Thompson, Science, 267:1456-1462(1995)].

Apoptotic cell death is typically accompanied by one or morecharacteristic morphological and biochemical changes in cells, such ascondensation of cytoplasm, loss of plasma membrane microvilli,segmentation of the nucleus, degradation of chromosomal DNA or loss ofmitochondrial function. A variety of extrinsic and intrinsic signals arebelieved to trigger or induce such morphological and biochemicalcellular changes [Raff, Nature, 356:397-400 (1992); Steller, Science,267:1445-1449 (1995); Sachs et al., Blood, 82:15 (1993)]. For instance,they can be triggered by hormonal stimuli, such as glucocorticoidhormones for immature thymocytes, as well as withdrawal of certaingrowth factors [Watanabe-Fukunaga et al., Nature, 356:314-317 (1992)].Also, some identified oncogenes such as myc, rel, and ElA, and tumorsuppressors, like p53, have been reported to have a role in inducingapoptosis. Certain chemotherapy drugs and some forms of radiation havelikewise been observed to have apoptosis-inducing activity [Thompson,supra].

Various molecules; such as tumor necrosis factor-α (“TNF-α”), tumornecrosis factor-fβ (“TNF-β” or “lymphotoxin”), CD30 ligand, CD27 ligand,CD40 ligand, OX-40 ligand, 4-1BB ligand, and Apo-1 ligand (also referredto as Fas ligand or CD95 ligand) have been identified as members of thetumor necrosis factor (“TNF”) family of cytokines [See, e.g., Gruss andDower, Blood, 85:3378-3404 (1995)]. Among these molecules, TNF-α, TNF-β,CD30 ligand, 4-1BB ligand, and Apo-1 ligand have been reported to beinvolved in apoptotic cell death. Both TNF-α and TNF-β have beenreported to induce apoptotic death in susceptible tumor cells [Schmid etal., Proc. Natl. Acad. Sci., 83:1881 (1986); Dealtry et al., Eur. J.Immunol., 17:689 (1987)]. Zheng et al. have reported that TNF-α isinvolved in post-stimulation apoptosis of CD8-positive T cells [Zheng etal., Nature, 377:348-351 (1995)]. Other investigators have reported thatCD30 ligand may be involved in deletion of self-reactive T cells in thethymus [Amakawa et al., Cold Spring Harbor Laboratory Symposium onProgrammed Cell Death, Abstr. No. 10, (1995)].

Mutations in the mouse Fas/Apo-1 receptor or ligand genes /(called 1prand gld, respectively) have been associated with some autoimmunedisorders, indicating that Apo-1 ligand may play a role in regulatingthe clonal deletion of self-reactive lymphocytes in the periphery[Krammer et al., Curr. Op. Immunol., 6:279-289 (1994); Nagata et al.,Science, 267:1449-1456 (1995)]: Apo-1 ligand is also reported to inducepost-stimulation apoptosis in CD4-positive T lymphocytes and in Blymphocytes, and may be involved in the elimination of activatedlymphocytes when their function is no longer needed, [Krammer et al.,supra; Nagata et al., supra]. Agonist mouse monoclonal antibodiesspecifically binding to the Apo-1 receptor have been reported to exhibitcell killing activity that is comparable to or similar to that of TNF-α[Yonehara et al., J. Exp. Med., 169:1747-1756 (1989)].

Induction of various cellular responses mediated by such TNF familycytokines is believed to be initiated by their binding to specific cellreceptors. Two distinct TNF receptors of approximately 55-kDa (TNF-R1)and 75-kDa (TNF-R2) have been identified [Hohman et al., J. Biol. Chem.,264:14927-14934 (1989); Brockhaus et al., Proc. Natl. Acad. Sci.,87:3127-3131 (1990); EP 417,563, published Mar.20, 1991] and human andmouse cDNAs corresponding to both receptor types have been isolated andcharacterized [Loetscher et al., Cell, 61:351 (1990); Schall et al.,Cell, 61:361 (1990); Smith et al., Science, 248:1019-1023 (1990); Lewiset al., Proc. Natl. Acad. Sci., 88:2830-2834 (1991); Goodwin et al.,Mol. Cell. Biol., 11:3020-3026 (1991)].

Itoh et al. discloe that the Apo-1 receptor can signal an apoptotic celldeath similar to that signaled by the 55-kDa TNF-R1 [Itoh et al.,supra]. Expression of the Apo-1 antigen has also been reported to bedown-regulated along with that of TNF-R1 when cells are treated witheither TNF-α or anti-Apo-1 mouse monoclonal antibody [Krammer et al.,supra; Nagata et al., supra]. Accordingly, some investigators havehypothesized that cell lines that co-express both Apo-1 and TNF-R1receptors may mediate cell killing through common signaling pathways[Id.].

The TNF family ligands identified to date, with the exception oflymphotoxin-a, are type II transmembrane proteins, whose C-terminus isextracellular. In contrast, the receptors in the TNF receptor (TNFR)family identified to date are type I transmembrane proteins. In both theTNF ligand and receptor families, however, homology identified betweenfamily members has been found mainly in the extracellular domain(“ECD”). Several of the TNF family cytokines, including TNF-α, Apo-1ligand and CD40 ligand, are cleaved proteolytically at the cell surface;the resulting protein in each case typically forms a homotrimericmolecule that functions as a soluble cytokine. TNF receptor familyproteins are also usually cleaved proteolytically to release solublereceptor. ECDs that can function as inhibitors of the cognate cytokines.For a review of the TNF family of cytokines and their receptors, seeGruss and Dower, supra.

SUMMARY OF THE INVENTION

Applicants have identified cDNA clones that encode a novel cytokine,designated “Apo-2 ligand.” It is presently believed that Apo-2 ligand isa member of the TNF cytokine family; Apo-2 ligand is related in aminoacid sequence to some known TNF-related proteins, including the Apo-1ligand. Applicants found, however, that the Apo-2 ligand is notinhibited appreciably by known soluble Apo-1 or TNF receptors, such asthe Fas/Apo-1, TNF-R1, or TNF-R2 receptors.

In one embodiment, the invention provides isolated biologically activeApo-2 ligand. In particular, the invention provides isolatedbiologically active human Apo-2 ligand, which in one embodiment,includes an amino acid sequence comprising residues 114-281 of FIG. 1A.In another embodiment, the Apo-2 ligand includes an amino acid sequencecomprising residues 41-281 or 15-281 of FIG. 1A. In another embodiment,the isolated biologically active human Apo-2 ligand includes an aminoacid sequence shown as residues 1-281 of FIG. 1A (SEQ ID NO:1).

In another embodiment, the invention provides chimeric moleculescomprising Apo-2 ligand fused to another, heterologous polypeptide. Anexample of such a chimeric molecule comprises the Apo-2 ligand fused toa tag polypeptide sequence.

In another embodiment, the invention provides an isolated nucleic acidmolecule encoding Apo-2 ligand. In one aspect, the nucleic acid moleculeis RNA or DNA that encodes a biologically active Apo-2 ligand or iscomplementary to nucleic acid sequence encoding such Apo-2 ligand, andremains stably bound to it under stringent conditions. In oneembodiment, the nucleic acid sequence is selected from:

(a) the coding region of the nucleic acid sequence of FIG. 1A that codesfor the full-length protein from residue 1 to residue 281 (i.e.,nucleotides 91 through 933), inclusive, or nucleotides 211 through 933that encodes for the extracellular protein from residue 41 to 281,inclusive, or nucleotides 430 through 933 that encodes for theextracellular protein from residue 114 to 281, inclusive, of the nucleicacid sequence shown in FIG. 1A (SEQ ID NO:2); or

(b) a sequence corresponding to the sequence of (a) within the scope ofdegeneracy of the genetic code.

In a further embodiment, the invention provides a replicable vectorcomprising the nucleic acid molecule encoding the Apo-2 ligand operablylinked to control sequences recognized by a host cell transfected ortransformed with the vector. A host cell comprising the vector or thenucleic acid molecule is also provided. A method of producing Apo-2ligand which comprises culturing a host cell comprising the nucleic acidmolecule and recovering the protein from the host cell culture isfurther provided.

In another embodiment, the invention provides an antibody which binds tothe Apo-2 ligand.

In another embodiment, the invention provides a composition comprisingbiologically active Apo-2 ligand and a pharmaceutically-acceptablecarrier. The composition may be a pharmaceutical composition useful forinducing or stimulating apoptosis.

In another embodiment, the invention provides a method for inducingapoptosis in mammalian cells, comprising exposing mammalian cells, invivo or ex vivo, to an amount of Apo-2 ligand effective for inducingapoptosis.

In another embodiment, the invention provides methods of treating amammal having cancer. In the methods, an effective amount of Apo-2ligand is administered to a mammal diagnosed as having cancer. The Apo-2ligand may also be administered to the mammal along with one or moreother therapies, such as chemotherapy, radiation therapy, or otheragents capable of inducing apoptosis.

A further embodiment of the invention provides articles of manufactureand kits that include Apo-2 ligand or Apo-2 ligand antibodies. Thearticles of manufacture and kits include a container, a label on thecontainer, and a composition contained within the container. The labelon the container indicates that the composition can be used for certaintherapeutic or non-therapeutic applications. The composition contains anactive agent, and the active agent comprises Apo-2 ligand or Apo-2ligand antibodies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows the nucleotide sequence of human Apo-2 ligand cDNA and itsderived amino acid sequence.

FIG. 1B shows an alignment of the C-terminal region of human Apo-2ligand with the corresponding region of known members of the human TNFcytokine family, 4-1BBL, OX4OL, CD27L, CD3OL, TNF-α, LT-β, LT-α, CD4OL,and Apo-1L.

FIGS. 1C-1E show (C) the cellular topology of the recombinant,full-length, C-terminal myc epitope-tagged Apo-2 ligand expressed inhuman 293 cells, as determined by FACS analysis using anti-epitopeantibody; (D) the size and subunit structure of recombinant, His₁₀epitope-tagged soluble Apo-2 expressed in recombinantbaculovirus-infected insect cells and purified by Ni²⁺-chelate affinitychromatography, as determined with (lanes 2, 3) or without (lane 1)chemical crosslinking followed by SDS-PAGE and silver staining; (E) thesize and subunit structure of recombinant, gD epitope-tagged, solubleApo-2 ligand expressed in metabolically labeled human 293 cells, asdetermined by immunoprecipitation with anti-epitope antibody, followedby SDS-PAGE and autoradiography.

FIGS. 2A-2E show the induction of apoptosis in B and T lymphocyte celllines by Apo-2 ligand. Apoptotic cells were identified by characteristicmorphological changes (A); by positive fluorescence staining withpropidium iodide (PI) and FITC-conjugated annexin V, measured by flowcytometry (B-D); and by analysis of internucleosomal DNA fragmentation(E).

FIGS. 3A-3C show the time course and the dose-dependence of Apo-2ligand-induced apoptosis and the lack of inhibition of Apo-2ligand-induced apoptosis by soluble receptor-IgG-fusion proteins basedon .the Fas/Apo-1 receptor, TNF-R1 receptor, or TNF-R2 receptor.

FIG. 4 shows the expression of Apo-2 ligand mRNA in human fetal andhuman adult tissues, as measured by Northern blot analysis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS I. Definitions

The terms “Apo-2 ligand” and “Apo-2L” are used herein to refer to apolypeptide sequence which includes amino acid residues 114-281,inclusive, residues 41-281, inclusive, residues 15-281, inclusive, orresidues 1-281, inclusive, of the amino acid sequence shown in FIG. 1A,as well as biologically active deletional, insertional, orsubstitutional variants of the above sequences. In a preferredembodiment, the polypeptide sequence has at least residues 114-281 ofFIG. 1A. In another preferred embodiment, the biologically activevariants have at least about 80% sequence identity, more preferably atleast about 90% sequence identity, and even more preferably, at leastabout 95% sequence identity with any one of the above sequences. Thedefinition encompasses Apo-2 ligand isolated from an Apo-2 ligandsource, such as from the human tissue types described herein (seeExample 8) or from another source, or prepared by recombinant orsynthetic methods. The present definition of Apo-2 ligand excludes knownEST sequences, such as GenBank HHEA47M, T90422, R31020, H43566, H44565,H44567, H54628, H44772, H54629, T82085, and T10524.

The term “epitope tagged” when used herein refers to a chimericpolypeptide comprising Apo-2 ligand, or a portion thereof, fused to a“tag polypeptide”. The tag polypeptide has enough residues to provide anepitope against which an antibody can be made, yet is short enough suchthat it does not interfere with activity of the Apo-2 ligand. The tagpolypeptide preferably also is fairly unique so that the antibody doesnot substantially cross-react with other epitopes. Suitable tagpolypeptides generally have at least six amino acid residues and usuallybetween about 8 to about 50 amino acid residues. (preferably, betweenabout 10 to about 20 residues).

“Isolated,” when'used to describe the various proteins disclosed herein,means protein that has been identified and separated and/or recoveredfrom a component of its natural environment. Contaminant components ofits natural environment are materials that would typically interferewith diagnostic or therapeutic uses for the protein, and may includeenzymes, hormones, and other proteinaceous or non-proteinaceous solutes.In preferred embodiments, the protein will be purified (1) to a degreesufficient to obtain at least 15 residues of N-terminal or internalamino acid sequence by use of a spinning cup sequenator, or (2) tohomogeneity by SDS-PAGE under non-reducing or reducing conditions usingCoomassie blue or, preferably, silver stain. Isolated protein includesprotein in situ within recombinant cells, since at least one componentof the Apo-2 ligand natural environment will not be present. Ordinarily,however, isolated protein will be prepared by at least one purificationstep.

An “isolated” Apo-2 ligand nucleic acid molecule is a nucleic acidmolecule that is identified and separated from at least one contaminantnucleic acid molecule with which it is ordinarily associated in thenatural source of the Apo-2 ligand nucleic acid. An isolated Apo-2ligand nucleic acid molecule is other than in the form or setting inwhich it is found in nature. Isolated Apo-2 ligand nucleic acidmolecules therefore are distinguished from the Apo-2 ligand nucleic acidmolecule as it exists in natural cells. However, an isolated Apo-2ligand nucleic acid molecule includes Apo-2 ligand nucleic acidmolecules contained in cells that ordinarily express Apo-2 ligand where,for example, the nucleic acid molecule is in a chromosomal locationdifferent from that of natural cells.

The term “control sequences” refers to DNA sequences necessary for theexpression of an operably linked coding sequence in a particular hostorganism. The control sequences that are suitable. for prokaryotes, forexample, include a promoter, optionally an operator sequence, and aribosome binding site. Eukaryotic cells are known to utilize promoters,polyadenylation signals, and enhancers.

Nucleic acid is “operably linked” when it is placed into a functionalrelationship with another nucleic acid sequence. For example, DNA for apresequence or secretory leader is operably linked to DNA for apolypeptide if it is expressed as a preprotein that participates in thesecretion of the polypeptide; a promoter or enhancer is operably linkedto a coding sequence if it affects the transcription of the sequence; ora ribosome binding site is operably linked to a coding sequence if it ispositioned so as to facilitate translation. Generally, “operably linked”means that the DNA sequences being linked are contiguous, and, in thecase of a secretory leader, contiguous and in reading phase. However,enhancers do not have to be contiguous. Linking is accomplished byligation at convenient restriction sites. If such sites do not exist,the synthetic oligonucleotide adaptors or linkers are used in accordancewith conventional practice.

The term “antibody” is used in the broadest sense and specificallycovers single anti-Apo-2 ligand monoclonal antibodies (including agonistand antagonist antibodies) and anti-Apo-2 ligand antibody compositionswith polyepitopic specificity.

The term “monoclonal antibody” as used herein refers to an antibodyobtained from a population of substantially homogeneous antibodies,i.e., the individual antibodies comprising the population are identicalexcept for possible naturally-occurring mutations that may be present inminor amounts. Monoclonal antibodies are highly specific, being directedagainst a single antigenic site. Furthermore, in contrast toconventional (polyclonal) antibody preparations which typically includedifferent antibodies directed against different determinants (epitopes),each monoclonal antibody is directed against a single determinant on theantigen.

The monoclonal antibodies herein include hybrid and recombinantantibodies produced by splicing a variable (including hypervariable)domain of an anti-Apo-2 ligand antibody with a constant domain (e.g.“humanized” antibodies), or a light chain with a heavy chain, or a chainfrom one species with a chain from another species, or fusions with,heterologous proteins, regardless of species of origin or immunoglobulinclass or subclass designation, as well as antibody fragments (e.g., Fab,F(ab′)₂, and Fv), so long as they exhibit the desired biologicalactivity. See, e.g. U.S. Pat. No. 4,816,567 and Mage et al., inMonoclonal Antibody Production Techniques and Applications, pp. 79-97(Marcel Dekker, Inc.: New York, 1987).

Thus, the modifier “monoclonal” indicates the character of the antibodyas being obtained from a substantially homogeneous population ofantibodies, and is not to be construed as requiring production of theantibody by any particular method. For example, the monoclonalantibodies to be used in accordance with the present invention may bemade by the hybridoma method first described by Kohler and Milstein,Nature, 256:495 (1975), or may be made by recombinant DNA methods suchas described in U.S. Pat. No. 4,816,567. The “monoclonal antibodies” mayalso be isolated from phage libraries generated using the techniquesdescribed in McCafferty et al., Nature, 348:552-554 (1990), for example.

“Humanized” forms of non-human (e.g. murine) antibodies are specificchimeric immunoglobulins, immunoglobulin chains, or fragments thereof(such as Fv, Fab, Fab′, F(ab′)₂ or other antigen-binding subsequences ofantibodies) which contain minimal sequence derived from non-humanimmunoglobulin. For the most part, humanized antibodies are humanimmunoglobulins (recipient antibody) in which residues from acomplementary determining region (CDR) of the recipient are replaced byresidues from a CDR of a non-human species (donor antibody) such asmouse, rat, or rabbit having the desired specificity, affinity, andcapacity: In some instances, Fv framework region (FR) residues of thehuman immunoglobulin are replaced by corresponding non-human residues.Furthermore, the humanized antibody may comprise residues which arefound neither in the recipient antibody nor in the imported CDR orframework sequences. These modifications are made to further refine andoptimize antibody performance. In general, the humanized antibody willcomprise substantially all of at least one, and typically two, variabledomains, in which all or substantially all of the CDR regions correspondto those of a non-human immunoglobulin and all or substantially all ofthe FR regions are those of a human immunoglobulin consensus sequence.The humanized antibody optimally also will comprise at least a portionof an immunoglobulin constant region (Fc), typically that of a humanimmunoglobulin.

“Biologically active” for the purposes herein means having the abilityto induce or stimulate apoptosis in at least one type of mammalian cellin vivo or ex vivo.

The terms “apoptosis” and “apoptotic activity” are used in a broad senseand refer to the orderly or controlled form of cell death in mammalsthat is typically accompanied by one or more characteristic cellchanges, including condensation of cytoplasm, loss of plasma membranemicrovilli, segmentation of the nucleus, degradation of chromosomal DNAor loss of mitochondrial function. This activity can be determined andmeasured, for instance, by cell viability assays, FACS analysis or DNAelectrophoresis.

The terms “cancer” and “cancerous” refer to or describe thephysiological condition in mammals that. is typically characterized byunregulated cell growth. Examples of cancer include but are not limitedto, carcinoma, lymphoma, leukemia, blastoma, and sarcoma. Moreparticular examples of such cancers include squamous cell carcinoma,small-cell lung cancer, non-small cell lung cancer, pancreatic cancer,glioblastoma multiforme, cervical cancer, stomach cancer, bladdercancer, hepatoma, breast cancer, colon carcinoma, and head and neckcancer. In a preferred embodiment, the cancer includes follicularlymphoma, carcinoma with p53 mutations, or hormone-dependent cancer suchas breast cancer, prostate cancer, or ovarian cancer.

The terms “treating,” “treatment,” and “therapy” as used herein refer tocurative therapy, ‘prophylactic therapy, and preventative therapy.

The term “mammal” as used herein refers to any mammal classified as .amammal, including humans, cows, horses, dogs and cats. In a preferredembodiment of the invention, the mammal is a human.

II. Compositions and Methods of the Invention

The present invention provides a novel cytokine related to the TNFligand family, the cytokine identified herein as “Apo-2 ligand.” Thepredicted mature amino acid sequence of human Apo-2 ligand contains 281amino acids, and has a calculated molecular weight of approximately 32.5kDa and an isoelectric point of approximately 7.63. There is no apparentsignal sequence at the N-terminus, although hydropathy analysisindicates the presence of a hydrophobic region between residues 15 and40. The absene of a signal sequence and the presence of an internalhydrophobic region suggests that Apo-2 ligand is a type II transmembraneprotein. A potential N-linked glycosylation site is located at residue109 in the putative extracellular region. The putative cytoplasmicregion comprises amino acid residues 1-14, the transmembrane regioncomprises amino acid residues 15-40 and the extracellular regioncomprises amino acid residues 41-281, shown in FIG. 1A. An Apo-2 ligandpolypeptide comprising amino acid residues 114-281 of the extracellularregion, shown in FIG. 1A, is also described in the Examples below.

A. Preparation of Apo-2 Ligand

The description below relates primarily to production of Apo-2 ligand byculturing cells transformed or transfected with a vector containingApo-2 ligand nucleic acid and recovering the polypeptide from the cellculture. It is of course, contemplated that alternative methods, whichare well known in the art, may be employed to prepare Apo-2 ligand,

1. Isolation of DNA Encoding Apo-2 Ligand

The DNA encoding Apo-2 ligand may be obtained from any cDNA libraryprepared from tissue believed to possess the Apo-2 ligand mRNA and toexpress it at a detectable level. Accordingly, human Apo-2 ligand DNAcan be conveniently obtained from a cDNA library prepared from humantissues, such as the bacteriophage library of human placental cDNAdescribed in Example 1. The Apo-2 ligand-encoding gene may also beobtained from a genomic library or by oligonucleotide synthesis.

Libraries can be screened with probes (such as antibodies to the Apo-2ligand or oligonucleotides of at least about 20-80 bases) designed toidentify the gene of interest or the protein encoded by it. Examples ofoligonucleotide probes are provided in Example 1. Screening the cDNA orgenomic library with the selected probe may be conducted using standardprocedures, such as described in Sambrook et al., Molecular Cloning: ALaboratory Manual (New York: Cold Spring Harbor Laboratory Press, 1989).An alternative means to isolate the gene encoding Apo-2 ligand is to usePCR methodology [Sambrook et al., supra; Dieffenbach et al., PCRPrimer:A Laboratory Manual (Cold Spring Harbor Laboratory Press, 1995)].

A preferred method of screening employs selected oligonucleotidesequences to screen cDNA libraries from various human tissues. Example 1below describes techniques for screening a cDNA library with twodifferent oligonucleotide probes. The oligonucleotide sequences selectedas probes should be of sufficient length and sufficiently unambiguousthat false positives are minimized. The oligonucleotide is preferablylabeled such that it can be detected upon hybridization to DNA in thelibrary being. screened. Methods of labeling are well known in the art,and include the use of radiolabels like ‘P-labeled ATP, biotinylation orenzyme labeling.

Nucleic acid having all the protein coding sequence may be obtained byscreening selected cDNA or genomic libraries using the deduced aminoacid sequence disclosed herein for the first time, and, if necessary,using conventional primer extension procedures as described in Sambrooket al., supra, to detect precursors and processing intermediates of mRNAthat may not have been reverse-transcribed into cDNA.

Amino acid sequence variants of Apo-2 ligand can be prepared byintroducing appropriate nucleotide changes into the Apo-2 ligand DNA, orby synthesis of the desired Apo-2 ligand polypeptide. Such variantsrepresent insertions, substitutions, and/or deletions of residues withinor at one or both of the ends of the intracellular region, thetransmembrane region, or the extracellular region, or of the amino acidsequence shown for the full-length .Apo-2 ligand in FIG. 1A. Anycombination of insertion, substitution, and/or deletion can be made toarrive at the final construct, provided that the final constructpossesses the desired apoptotic activity as defined herein. In apreferred embodiment, the variants have at least about 80% sequenceidentity, more preferably, at least about 90% sequence identity, andeven more preferably, at least about 95% sequence identity with thesequences identified herein for the intracellular, transmembrane, orextracellular regions of Apo-2 ligand, or the full-length sequence forApo-2 ligand. The amino acid changes also may alter post-translationalprocesses of the Apo-2 ligand, such as changing the number or positionof glycosylation sites or altering the membrane anchoringcharacteristics.

Variations in the native sequence as described above can be made usingany of the techniques and guidelines for conservative andnon-conservative mutations set forth in U.S. Pat. No. 5,364,934. Theseinclude oligonucleotide-mediated (site-directed) mutagenesis, alaninescanning, and PCR mutagenesis.

2. Insertion of Nucleic Acid into A Replicable Vector

The nucleic acid (e.g., cDNA or genomic DNA) encoding native or variantApo-2 ligand may be inserted into a replicable vector for furthercloning (amplification of the DNA) or for expression. Various vectorsare publicly available. The vector components generally include, but arenot limited to, one or more of the following: a signal sequence, anorigin of replication, one or more marker genes, an enhancer element, apromoter, and a transcription termination sequence, each of which isdescribed below.

(i) Signal Sequence Component

The Apo-2 ligand may be produced recombinantly not only directly, butalso as a fusion polypeptide with a heterologous polypeptide, which maybe a signal sequence or other polypeptide having a specific cleavagesite at the N-terminus of the mature protein or polypeptide. In general,the signal sequence may be a component of the vector, or it may be apart of the Apo-2 ligand DNA that is inserted into the vector. Theheterologous signal sequence selected preferably is one that isrecognized and processed (i.e., cleaved by a signal peptidase) by thehost cell. The signal sequence may be a prokaryotic signal sequenceselected, for example, from the group of the alkaline phosphatase,penicillinase, 1pp, or heat-stable enterotoxin II leaders. For yeastsecretion the signal sequence may be, e.g., the yeast invertase leader,alpha factor leader (including Saccharomyces and Kluyveromyces α-factorleaders, the latter described in U.S. Pat. No. 5,010,182), or acidphosphatase leader, the C. albicans glucoamylase leader (EP 362,179published 4 Apr. 1990), or the signal described in WO 90/13646 published15 Nov. 1990. In mammalian cell expression the native Apo-2 ligandpresequence that normally directs insertion of Apo-2 ligand in the cellmembrane of human cells in vivo is satisfactory, although othermammalian signal sequences may be used to direct secretion of theprotein, such as signal sequences from secreted polypeptides of the sameor related species, as well as viral secretory leaders, for example, theherpes simplex glycoprotein D signal.

The DNA for such precursor region is preferably ligated in reading frameto DNA encoding Apo-2 ligand.

(ii) Origin of Replication Component

Both expression and cloning vectors contain a nucleic acid sequence thatenables the vector to replicate in one or more selected host cells.Generally, in cloning vectors this sequence is one that enables thevector to replicate independently of the host chromosomal DNA, andincludes origins of replication or autonomously replicating sequences.Such sequences are well known for a variety of bacteria, yeast, andviruses. The origin of replication from the plasmid pBR322 is suitablefor most Gram-negative bacteria, the 2p plasmid origin is suitable foryeast, and various viral origins (SV40, polyoma, adenovirus, VSV or BPV)are useful for cloning vectors in mammalian cells. Generally, the originof replication component is not needed for mammalian expression vectors(the SV40 origin may typically be used because it contains the earlypromoter).

Most expression vectors are “shuttle” vectors, i.e., they are capable ofreplication in at least one class of organisms but can be transfectedinto another organism for expression. For example, a vector is cloned inE. coli and then the same vector is transfected into yeast or mammaliancells for expression even though it is not capable of replicatingindependently of the host cell chromosome.

DNA may also be amplified by insertion into the host genome. This isreadily accomplished using Bacillus species as hosts, for example, byincluding in the vector a DNA sequence that is complementary to asequence found in Bacillus genomic DNA. Transfection of Bacillus withthis vector results in homologous recombination with the genome andinsertion of Apo-2 ligand DNA. However, the recovery of genomic DNAencoding Apo-2 ligand is more S complex than that of an exogenouslyreplicated vector because restriction enzyme digestion is required toexcise the Apo-2 ligand DNA.

(iii) Selection Gene Component

Expression and cloning vectors typically contain a selection gene, alsotermed a selectable marker. This gene encodes a protein necessary forthe survival or growth of transformed host cells grown in a selectiveculture medium. Host cells not transformed with the vector containingthe selection gene will not survive in the culture medium. Typicalselection genes encode proteins that (a) confer resistance toantibiotics or other toxins, e.g., ampicillin, neomycin, methotrexate,or tetracycline, (b) complement auxotrophic deficiencies, or (c) supplycritical nutrients not available from complex media, e.g., the.geneencoding D-alanine racemase for Bacilli.

One example of a selection scheme utilizes a drug to arrest growth of ahost cell. Those cells that are successfully transformed with aheterologous gene produce a protein conferring drug resistance and thussurvive the selection regimen. Examples of such dominant selection usethe drugs neomycin [Southern et al., J. Molec. Appl. Genet., 1:327(1982)], mycophenolic acid (Mulligan et al., Science, 209:1422(1980)] orhygromycin [Sugden et al., Mol. Cell. Biol., 5:410-413 (1985)]. Thethree examples given above employ bacterial genes under eukaryoticcontrol to convey resistance to the appropriate drug G418 or neomycin(geneticin), xgpt (mycophenolic acid), or hygromycin, respectively.

Another example of suitable selectable markers for mammalian cells arethose that enable the identification of cells competent to take up theApo-2 ligand nucleic acid, such as DHFR or thymidine kinase. Themammalian cell transformants are placed under selection pressure thatonly the transformants are uniquely adapted to survive by virtue ofhaving taken up the marker. Selection pressure is imposed by culturingthe transformants under conditions in which the concentration ofselection agent in the medium is successively changed, thereby leadingto amplification of both the selection gene and the DNA that encodesApo-2 ligand. Amplification is the process by which genes in greaterdemand for the production of a protein critical for growth arereiterated in tandem within the chromosomes of successive generations ofrecombinant cells. Increased quantities of Apo-2 ligand are synthesizedfrom the amplified DNA. Other examples of amplifiable genes includemetallothionein-I and -II, adenosine deaminase, and ornithinedecarboxylase.

Cells transformed with the DHFR selection gene may first be identifiedby culturing all of the<transformants in a culture medium that containsmethotrexate (Mtx), a competitive antagonist of DHFR. An appropriatehost cell when wild-type DHFR is employed is the Chinese hamster ovary(CHO) cell line deficient in DHFR activity, prepared and propagated asdescribed by Urlaub et al., Proc. Natl. Acad. Sci. USA, 77:4216 (1980).The transformed cells are then exposed to increased levels ofmethotrexate. This leads to the synthesis of multiple copies of the DHFRgene, and, concomitantly, multiple copies of other DNA comprising theexpression vectors, such as the DNA encoding Apo-2 ligand. Thisamplification technique can be used with any otherwise suitable host,e.g., ATCC No. CCL61 CHO-K1, notwithstanding the presence of endogenousDHFR if, for example, a mutant DHFR gene that is highly resistant to Mtxis employed (EP 117,060).

Alternatively, host cells (particularly wild-type hosts that containendogenous DHFR) transformed or co-transformed with DNA sequencesencoding Apo-2 ligand, wild-type DHFR protein, and another selectablemarker such as aminoglycoside 3′-phosphotransferase (APH) can beselected by cell growth in medium containing a selection agent for theselectable marker such as an aminoglycosidic antibiotic, e.g.,kanamycin, neomycin, or G418. See U.S. Pat. No. 4,965,199.

A suitable selection gene for use in yeast is the trpl gene present inthe yeast plasmid YRp7 [Stinchcomb et al., Nature, 282:39 (1979);Kingsman et al., Gene, 7:141 (1979); Tschemper et al., Gene, 10:157(1980)]. The trpl gene provides a selection marker for a mutant strainof yeast lacking the ability to grow in tryptophan, for example, ATCCNo. 44076 or PEP4-1 [Jones, Genetics, 85:12 (1977)]. The presence of thetrpl lesion. in the yeast host cell genome then provides an effectiveenvironment for detecting transformation by growth in the absence oftryptophan. Similarly, Leu2-deficient yeast strains (ATCC 20,622 or38,626) are complemented by known plasmids bearing the Leu2 gene.

In addition, vectors derived from the 1.6 Am circular plasmid pKD1 canbe used for transformation of Kluyveromyces yeasts [Bianchi et al.,Curr. Genet., 12:185 (1987)]. More recently, an expression system for,large-scale production of recombinant calf chymosin was reported for K.lactis [Van den Berg, Bio/Technoloqy, 8:135 (1990)]. Stable multi-copyexpression vectors for secretion of mature recombinant human serumalbumin by industrial strains of Kluyveromyces have also been disclosed[Fleer et al., Bio/Technology, 9:968-975 (1991)].

(iv) Promoter Component

Expression and cloning vectors usually contain a promoter, that isrecognized by the host organism and is operably linked to the Apo-2ligand nucleic acid sequence. Promoters are untranslated sequenceslocated upstream (5′) to the start codon of a structural gene (generallywithin about 100 to 1000 bp) that control the transcription andtranslation of particular nucleic acid sequence, such as the Apo-2ligand nucleic acid sequence, to which they are operably linked. Suchpromoters typically fall into two classes, inducible and constitutive.Inducible promoters are promoters that initiate increased levels oftranscription from DNA under their control in response to some change inculture conditions, e.g., the presence or absence of a nutrient or achange in temperature. At this time a large number of promotersrecognized by a variety of potential host cells are well known. Thesepromoters are operably linked to Apo-2 ligand encoding DNA by removingthe promoter from the source DNA by restriction enzyme digestion andinserting the isolated promoter sequence into the vector. Both thenative Apo-2 ligand promoter sequence and many heterologous promotersmay be used to direct amplification and/or expression of the Apo-2ligand DNA.

Promoters suitable for use with prokaryotic hosts include theβ-lactamase and lactose promoter systems [Chang et al., Nature, 275:615(1978); Goeddel et al., Nature, 281:544 (1979)], alkaline phosphatase, atryptophan (trp) promoter system [Goeddel, Nucleic Acids Res., 8:4057(1980); EP 36,776], and hybrid promoters such as the tac promoter[deBoer et al., Proc. Natl. Acad. Sci. USA, 80:21-25 (1983)]. However,other known bacterial promoters are suitable. Their nucleotide sequenceshave been published, thereby enabling a skilled worker operably toligate them to DNA encoding Apo-2 ligand [Siebenlist et al., Cell,20:269 (1980)] using linkers or adaptors to supply any requiredrestriction sites. Promoters for use in bacterial systems also willcontain a Shine-Dalgarno (S.D.) sequence operably linked to the DNAencoding Apo-2 ligand.

Promoter sequences are known for eukaryotes. Virtually all eukaryoticgenes have an AT-rich region located approximately to 30 bases upstreamfrom the site where transcription is initiated. Another sequence found70 to 80 bases upstream from the start of transcription of many genes isa CXCAAT region where X may be any nucleotide. At the 3′ end of mosteukaryotic genes is an AATAAA sequence that may be the signal foraddition of the poly A tail to the 3′ end of the coding sequence. All ofthese sequences are suitably inserted into eukaryotic expressionvectors.

Examples of suitable promoting sequences for use with yeast hostsinclude the promoters for 3-phosphoglycerate kinase [Hitzeman et al., J.Biol. Chem., 255:2073 (1980)] or other glycolytic enzymes [Hess et al.,J. Adv. Enzyme Reg., 7:149 (1968); Holland, Biochemistry, 17:4900(1978)], such as enolase, glyceraldehyde-3-phosphate dehydrogenase,hexokinase, pyruvate decarboxylase, phosphofructokinase,glucose-6-phosphate isomerase, 3-phosphoglycerate mutase, pyruvatekinase, triosephosphate isomerase, phosphoglucose isomerase, andglucokinase.

Other yeast promoters, which are inducible promoters having theadditional advantage of transcription controlled by growth conditions,are the promoter regions for alcohol dehydrogenase 2, isocytochrome C,acid phosphatase, degradative enzymes associated with nitrogenmetabolism, metallothionein, glyceraldehyde-3-phosphate dehydrogenase,and enzymes responsible for maltose and galactose utilization. Suitablevectors and promoters for use in yeast expression are further describedin EP 73,657. Yeast enhancers also are advantageously used with yeastpromoters.

Apo-2 ligand transcription from vectors in mammalian host cells iscontrolled, for example, by promoters obtained from the genomes ofviruses such as polyoma virus, fowlpox virus (UK 2,211,504 published 5Jul. 1989), adenovirus (such as Adenovirus 2), bovine papilloma virus,avian sarcoma virus, cytomegalovirus, a retrovirus, hepatitis-B virusand most preferably Simian Virus 40 (SV40), from heterologous mammalianpromoters, e.g., the actin promoter or an immunoglobulin promoter, fromheat-shock promoters, and from the promoter normally associated with theApo-2 ligand sequence, provided such promoters are compatible with thehost cell systems.

The early and late promoters of the SV40 virus are 25′ convenientlyobtained as an SV40 restriction fragment that also contains the SV40viral origin of replication [Fiers et al., Nature, 273:113 (1978);Mulligan and Berg, Science, 209:1422-1427 (1980); Pavlakis et al., Proc.Natl. Acad. Sci. USA, 78:7398-7402 (1981)]. The immediate early promoterof the human cytomegalovirus is conveniently obtained as a HindIII Erestriction fragment [Greenaway et al., Gene, 18:355-360 (1982)]. Asystem for expressing DNA in mammalian hosts using the bovine papillomavirus as a vector is disclosed in U.S. Pat. No. 4,419,446. Amodification of this system is described in U.S. Pat. No. 4,601,978 [Seealso Gray et al., Nature, 295:503-508 (1982) on expressing cDNA encodingimmune interferon in monkey cells; Reyes et al., Nature, 297:598-601(1982) on expression of human β-interferon cDNA in mouse cells under thecontrol of a thymidine kinase promoter from herpes simplex virus;Canaani and Berg, Proc. Natl. Acad. Sci. USA 79:5166-5170 (1982) onexpression of the human interferon β1 gene in cultured mouse and rabbitcells; and Gorman et al., Proc. Natl. Acad. Sci. USA, 79:6777-6781(1982) on expression of bacterial CAT sequences in. CV-1 monkey kidneycells, chicken embryo fibroblasts, Chinese hamster ovary cells, HeLacells, and mouse NIH-3T3 cells using the Rous sarcoma virus longterminal repeat as a promoter].

(v) Enhancer Element Component

Transcription of a DNA encoding the Apo-2 ligand of this invention byhigher eukaryotes may be increased by inserting an enhancer sequenceinto the vector. Enhancers are cis-acting elements of DNA, usually aboutfrom 10 to 300 bp, that act on a promoter to increase its transcription.Enhancers are relatively orientation and position independent, havingbeen found 5′ [Laimins et al., Proc. Natl. Acad. Sci. USA, 78:993(1981]) and 3′ [Lusky et al., Mol. Cell Bio., 3:1108 (1983]) to thetranscription unit, within an intron [Banerji et al., Cell, 33:729(1983)], as well as within the coding sequence itself [Osborne et al.,Mol. Cell Bio., 4:1293 (1984)]. Many enhancer sequences are now knownfrom mammalian genes (globin, elastase, albumin, α-fetoprotein, andinsulin). Typically, however, one will use an enhancer from a eukaryoticcell virus. Examples include the SV40 enhancer on the late side of thereplication origin (bp 100-270), the cytomegalovirus early promoterenhancer, the polyoma enhancer on the late side of the replicationorigin, and adenovirus enhancers. See also Yaniv, Nature, 297:17-18(1982) on enhancing elements for activation of eukaryotic promoters. Theenhancer may be spliced into the vector at a position 5′ or 3′ to theApo-2 ligand-encoding sequence, but is preferably located at a site 5′from the promoter.

(vi) Transcription Termination Component

Expression vectors used in eukaryotic host cells (yeast, fungi, insect,plant, animal, human, or nucleated cells from other multicellularorganisms) will also containsequences necessary for the termination oftranscription and for stabilizing the mRNA. Such sequences are commonlyavailable from the 5′ and, occasionally 3′, untranslated regions ofeukaryotic or viral DNAs or cDNAs. These regions contain nucleotidesegments transcribed as polyadenylated fragments in the untranslatedportion of the mRNA encoding Apo-2 ligand.

(vii) Construction and Analysis of Vectors

Construction of suitable vectors containing one or more of theabove-listed components employs standard ligation techniques. Isolatedplasmids or DNA fragments are cleaved, tailored, and re-ligated in theform desired to generate the plasmids required.

For analysis,to confirm correct sequences in plasmids constructed, theligation mixtures can be used to transform E. coli K12 strain 294 (ATCC31,446) and successful transformants selected by ampicillin ortetracycline resistance where appropriate. Plasmids from thetransformants are prepared, analyzed by restriction endonucleasedigestion, and/or sequenced by the method of Messing et al., NucleicAcids Res., 9:309 (1981) or by the method of Maxam et al., Methods inEnzymology, 65:499 (1980).

(viii) Transient Expression Vectors

Expression vectors that provide for the transient expression inmammalian cells of DNA encoding Apo-2 ligand may be employed. Ingeneral, transient expression involves the use of an expression vectorthat is able to replicate efficiently in a host cell, such that the hostcell accumulates many copies of the expression vector and, in turn,synthesizes high levels of a desired polypeptide encoded by theexpression vector [Sambrook et al., supra]. Transient expressionsystems, comprising a suitable expression vector and a host cell, allowfor the convenient positive identification of polypeptides encoded bycloned DNAs, as well as for the rapid screening of such polypeptides fordesired biological or physiological properties. Thus, transientexpression systems are particularly useful in the invention for purposesof identifying analogs and variants of Apo-2 ligand that arebiologically active Apo-2 ligand.

(ix) Suitable Exemplary Vertebrate Cell Vectors

Other methods, vectors, and host cells suitable for adaptation to thesynthesis of Apo-2 ligand in recombinant vertebrate cell culture aredescribed in Gething et al., Nature, 293:620-625 (1981); Mantei et al.,Nature, 281:40-46 (1979); EP 117,060; and EP 117,058. A particularlyuseful plasmid for mammalian cell culture expression of Apo-2 ligand ispRK5 [EP 307,247; also described in Example 1] or pSVI6B [WO 91/08291published 13 Jun. 1991].

3. Selection and Transformation of Host Cells

Suitable host cells for cloning or expressing the DNA in the vectorsherein are the prokaryote, yeast, or higher eukaryote cells describedabove. Suitable prokaryotes for this purpose include but are not limitedto eubacteria, such as Gram-negative or Gram-positive organisms, forexample, Enterobacteriaceae such as Escherichia, e.g., E. coli,Enterobacter, Erwinia, Klebsiella, Proteus, Salmonella, e.g., Salmonellatyphimurium, Serratia, e.g., Serratia marcescans, and Shigella, as wellas Bacilli such as B. subtilis and B. licheniformis (e.g., B.licheniformis 41P disclosed in DD 266,710 published 12 Apr. 1989),Pseudomonas such as P. aeruginosa, and Streptomyces. Preferably, thehost cell should secrete minimal amounts of proteolytic enzymes.

In addition to prokaryotes, eukaryotic microbes such as filamentousfungi or yeast are suitable cloning or expression hosts for Apo-2ligand-encoding vectors. Saccharomyces cerevisiae, or common baker'syeast, is the most commonly used among lower eukaryotic hostmicroorganisms. However, a number of other genera, species, and strainsare commonly available and useful herein.

Suitable host cells for the expression of glycosylated Apo-2 ligand arederived from multicellular organisms. Such host cells are capable ofcomplex processing and glycosylation activities. In principle, anyhigher eukaryotic cell culture is workable, whether from vertebrate orinvertebrate culture. Examples of invertebrate cellsinclude plant andinsect cells. Numerous baculoviral strains and variants andcorresponding permissive insect host cells from hosts such as Spodopterafrugiperda (caterpillar), Aedes aegypti (mosquito), Aedes albopictus(mosquito), Drosophila melanogaster (fruitfly), and Bombyx mori havebeen identified [See, e.g., Luckow et al., Bio/Technology, 6:47-55(1988); Miller et al., in Genetic Engineering, Setlow et al., eds., Vol.8 (Plenum Publishing, 1986), pp. 277-279; and Maeda et al., Nature,315:592-594 (1985)]. A variety of viral strains for transfection arepublicly available, e.g., the L-1 variant of Autographa californica NPVand the Bm-5 strain of Bombyx mori NPV, and such viruses may be used asthe virus herein according to the present invention, particularly fortransfection of Spodoptera frugiperda (“Sf9”) cells, described inExample 2.

Plant cell cultures of cotton, corn, potato, soybean, petunia, tomato,and tobacco can be utilized as hosts. Typically, plant cells aretransfected by incubation with certain strains of the bacteriumAgrobacterium tumefaciens, which has been previously manipulated tocontain the Apo-2 ligand-encoding DNA. During incubation of the plantcell culture with A. tumefaciens, the DNA encoding the Apo-2 ligand istransferred to the plant cell host such that it is transfected, andwill, under appropriate conditions, express the Apo-2 ligand-encodingDNA. In addition, regulatory and signal sequences compatible with plantcells are available, such as the nopaline synthase promoter andpolyadenylation signal sequences [Depicker et al., J. Mol. Appl. Gen.,1:561 (1982)]. In addition,. DNA segments isolated from the upstreamregion of the T-DNA 780 gene are capable of activating or increasingtranscription levels of plant-expressible genes in recombinantDNA-containing plant tissue [EP 321,196 published 21 Jun. 1989].

Propagation of vertebrate cells in culture (tissue culture) is also wellknown in the art [See, e.g., Tissue Culture, Academic Press, Kruse andPatterson, editors (1973)]. Examples of useful mammalian host cell linesare monkey kidney CV1 line transformed by SV40 (COS-7, ATCC CRL 1651);human embryonic kidney line (293 or 293 cells subcloned for growth insuspension culture, Graham et al., J. Gen Virol., 36:59 (1977)); babyhamster kidney cells (BHK, ATCC CCL 10); Chinese hamster ovarycells/-DHFR (CHO, Urlaub and Chasin, Proc. Natl. Acad. Sci. USA, 77:4216(1980)); mouse sertoli cells (TM4, Mather, Biol. Reprod., 23:243-251(1980)); monkey kidney cells (CV1 ATCC CCL 70); African green monkeykidney cells (VERO-76, ATCC CRL-1587); human cervical carcinoma cells(HELA, ATCC CCL ‘2); canine kidney cell (MDCK, ATCC CCL 34); buffalo ratliver cells (BRL 3A, ATCC CRL 1442); human lung cells (W138, ATCC CCL7E); human liver cells (Hep G2, HB 8065); mouse mammary tumor (MMT060562, ATCC CCL51); TRI cells (Mather et al., Annals N.Y. Acad. Sci.,383:44-68 (1982)); MRC 5 cells; and FS4 cells.

Host cells are transfected and preferably transformed with theabove-described expression or cloning vectors for Apo-2 ligandproduction and cultured in conventional nutrient media modified asappropriate for inducing promoters, selecting transformants, oramplifying the genes encoding the desired sequences.

Transfection refers to the taking up of an expression vector by a hostcell whether or not any coding sequences are in fact expressed. Numerousmethods of transfection are known to the ordinarily skilled artisan, forexample, CaPO₄ and electroporation. Successful transfection is generallyrecognized when any indication of the operation of this vector occurswithin the host cell.

Transformation means introducing DNA into an organism so that the DNA isreplicable, either as an extrachromosomal element or by chromosomalintegrant. Depending on the host cell used, transformation is done usingstandard techniques appropriate to such cells. The calcium treatmentemploying calcium chloride, as described in Sambrook et al., supra, orelectroporation is generally used for prokaryotes or other cells thatcontain substantial cell-wall barriers. Infection with Agrobacteriumtumefaciens is used for transformation of certain plant cells, asdescribed by Shaw et al., Gene, 23:315 (1983) and WO 89/05859 published29 Jun. 1989. In addition, plants may be transfected using ultrasoundtreatment as described in WO'91/00358 published 10 Jan. 1991.

For mammalian cells without such cell walls, the calcium phosphateprecipitation method of Graham and van der Eb, Virology, 52:456-457(1978) is preferred. General aspects of mammalian cell host systemtransformations have been described in U.S. Pat. No. 4,399,216.Transformations into yeast are typically carried out according to themethod of Van Solingen et al., J. Bact., 130:946 (1977) and Hsiao etal., Proc. Natl. Acad. Sci. (USA), 76:3829 (1979). However, othermethods for introducing DNA into cells, such as by nuclearmicroinjection, electroporation, bacterial protoplast fusion with intactcells, or polycations, e.g., polybrene, polyornithine, may also be used.For various techniques for transforming mammalian cells, see Keown etal., Methods in Enzymology, 185:527-537. (1990) and Mansour et al.,Nature, 336:348-352 (1988).

4. Culturing the Host Cells

Prokaryotic cells used to produce Apo-2 ligand may be cultured insuitable media as described generally in Sambrook et al., supra.

The mammalian host cells used to produce Apo-2 ligand may be cultured ina variety of media. Examples of commercially available media includeHam's F10 (Sigma), Minimal Essential Medium (“MEM”, Sigma), RPMI-1640(Sigma), and Dulbecco's Modified Eagle's

Medium (“DMEM”, Sigma). Any such media may be supplemented as necessarywith hormones and/or other growth factors (such as insulin, transferrin,or epidermal growth factor), salts (such as sodium chloride, calcium,magnesium, and phosphate), buffers (such as HEPES), nucleosides (such asadenosine and thymidine), antibiotics (such as Gentamycin™ drug), traceelements (defined as inorganic compounds usually present at finalconcentrations in the micromolar range), and glucose or an equivalentenergy source. Any other necessary supplements may also be included atappropriate concentrations that would be known to those skilled in theart. The culture conditions, such as temperature, pH, and the like, arethose previously used with the host cell selected for expression, andwill be apparent to the ordinarily skilled artisan.

In general, principles, protocols, and practical techniques formaximizing the productivity of mammalian cell cultures can be found inMammalian Cell Biotechnology: a Practical Approach, M. Butler, ed. (IRLPress, 1991).

The host cells referred to in this disclosure encompass cells in cultureas well as cells that are within a host animal.

5. Detecting Gene Amplification/Expression

Gene amplification and/or expression may be measured in a sampledirectly, for example, by conventional Southern blotting, Northernblotting to quantitate the transcription of mRNA [Thomas, Proc. Natl.Acad. Sci. USA, 77:5201-5205 (1980)), dot blotting (DNA analysis), or insitu hybridization, using an appropriately labeled probe, based on thesequences provided herein. Various labels may be employed, most commonlyradioisotopes, and particularly ³²P. However, other techniques may alsobe employed, such as using biotin-modified nucleotides for introductioninto a polynucleotide. The biotin then serves as the site for binding toravidin or antibodies, which may be labeled with a wide variety oflabels, such as radionucleotides, fluorescers or enzymes. Alternatively,antibodies may be employed that can recognize specific duplexes,including DNA duplexes, RNA duplexes, and DNA-RNA hybrid duplexes orDNA-protein duplexes. The antibodies in turn may be labeled and theassay may be carried out where the duplex is bound to a surface, so thatupon the formation of duplex on the surface, the presence of antibodybound to the duplex can be detected.

Gene expression, alternatively, may be measured by immunologicalmethods, such as immunohistochemical staining of cells or tissuesections and assay of cell culture or body fluids, to quantitatedirectly the expression of gene product. With immunohistochemicalstaining techniques, a cell sample is prepared, typically by dehydrationand fixation, followed by reaction with labeled antibodies specific forthe gene product coupled, where the labels are usually visuallydetectable, such as enzymatic labels, fluorescent labels, luminescentlabels, and the like.

Antibodies useful for immunohistochemical staining and/or assay ofsample fluids may be either monoclonal or polyclonal, and may beprepared in any mammal. Conveniently, the antibodies may be preparedagainst a native Apo-2 ligand polypeptide or against a synthetic peptidebased on the DNA sequences provided herein or against exogenous sequencefused to Apo-2 ligand DNA and encoding a specific antibody epitope.

6. Purification of Apo-2 Ligand Polypeptide

Apo-2 ligand preferably is recovered from the culture medium as asecreted polypeptide, although it also may be recovered from host celllysates when directly produced without a secretory signal. If the Apo-2ligand is membrane-bound, it can be released from the membrane using asuitable detergent solution (e.g. Triton-X 100) or its extracellularregion may be released by enzymatic cleavage.

When Apo-2 ligand is produced in a. recombinant cell other than one ofhuman origin, the Apo-2 ligand is free of proteins or polypeptides ofhuman origin. However, it is usually necessary to purify Apo-2 ligandfrom recombinant cell proteins or polypeptides to obtain preparationsthat are substantially homogeneous as to Apo-2 ligand. As a first step,the culture medium or lysate may be centrifuged to remove particulatecell debris. Apo-2 ligand thereafter is purified from contaminantsoluble proteins and polypeptides, with the following procedures beingexemplary of suitable purification procedures: by fractionation on anion-exchange column; ethanol precipitation; reverse phase HPLC;chromatography on silica or on a cation-exchange resin such as DEAE;chromatofocusing; SDS-PAGE; ammonium sulfate precipitation; gelfiltration using, for example, Sephadex G-75; and protein A Sepharosecolumns to remove contaminants such as IgG.

In a preferred embodiment, the Apo-2 ligand can be isolated byaffinity⁻chromatography, as described in Example 3.

Apo-2 ligand variants in which residues have been deleted, inserted, orsubstituted are recovered in the same fashion as native Apo-2 ligand,taking account of any substantial, changes in properties occasioned bythe variation. For example, preparation of an Apo-2 ligand fusion withanother protein or polypeptide, e.g., a bacterial or viral antigen,facilitates purification; an immunoaffinity column containing antibodyto the antigen can be used to adsorb the fusion polypeptide. In apreferred embodiment, an extracellu]ar sequence of Apo-2 ligand is fusedto a His₁₀ peptide and purified by Ni’-chelate affinity chromatography.

A protease inhibitor such as phenyl methyl sulfonyl fluoride (PMSF) alsomay be useful to inhibit proteolytic degradation during purification,and antibiotics may be included to prevent the growth of adventitiouscontaminants. One skilled in the art will appreciate that purificationmethods suitable for native Apo-2 ligand may require modification toaccount for changes in the character of Apo-2 ligand or its variantsupon expression in recombinant cell culture.

7. Covalent Modifications of Apo-2 Ligand Polypeptides

Covalent modifications of Apo-2 ligand are included within the scope ofthis invention. Both native Apo-2 ligand and amino acid sequencevariants of the Apo-2 ligand may be covalently modified. One type ofcovalent modification of the Apo-2 ligand is introduced into themolecule by reacting targeted amino acid residues of the Apo-2 ligandwith an organic derivatizing agent that is capable of reacting withselected side chains or the N- or C-terminal residues of the Apo-2ligand.

Derivatization with bifunctional agents is useful for crosslinking Apo-2ligand to a water-insoluble support matrix or surface for use in themethod for purifying anti-Apo-2 ligand antibodies, and vice-versa.Commonly used crosslinking agents include, e.g.,1,1-bis(diazoacetyl)-2-phenylethane, glutaraldehyde,N-hydroxysuccinimide esters, for example, esters with 4-azido-salicylicacid, homobifunctional imidoesters, including disuccinimidyl esters suchas 3,3′-dithiobis(succinimidyl-propionate), and bifunctional maleimidessuch as bis-N-maleimido-1,8-octane. Derivatizing agents such asmethyl-3-[(p-azidophenyl)-dithio]propioimidate yield photoactivatableintermediates that are capable of forming crosslinks in the presence oflight. Alternatively, reactive water-insoluble matrices such as cyanogenbromide-activated carbohydrates, and the reactive substrates describedin U.S. Pat. Nos. 3,969,287; 3,691,016; 4,195,128; 4,247,642; 4,229,537;and 4,330,440 are employed for protein immobilization.

Other modifications include deamidation of glutaminyl and asparaginylresidues to the corresponding glutamyl and aspartyl residues,respectively, hydroxylation of proline and lysine, phosphorylation ofhydroxyl groups of seryl or threonyl residues, methylation of theα-amino groups of lysine, arginine, and histidine side chains [T. E.Creighton, Proteins: Structure and Molecular Properties, W. H. Freeman &Co., San Francisco, pp. 79-86 (1983)], acetylation of the N-terminalamine, and amidation of any C-terminal carboxyl group. The modifiedforms of the residues fall within the scope of the present invention.

Another type of covalent modification of the Apo-2 ligand polypeptideincluded within the scope of this invention comprises altering thenative glycosylation pattern of the polypeptide. “Altering the nativeglycosylation pattern” is intended for purposes herein to mean deletingone or more carbohydrate moieties found in native Apo-2 ligand, and/oradding one or more glycosylation sites that are not present in thenative Apo-2 ligand.

Glycosylation of polypeptides is typically either N-linked or O-linked.N-linked refers to the attachment of the carbohydrate moiety to the sidechain of an asparagine residue. The tripeptide sequencesasparagine-X-serine and asparagine-X-threonine, where X is any aminoacid except proline, are the recognition sequences for enzymaticattachment of the carbohydrate moiety to the asparagine side chain.Thus, the presence of either of these tripeptide sequences in apolypeptide creates a potential glycosylation site. O-linkedglycosylation refers to the attachment of one of the sugarsN-aceylgalactosamine, galactose, or xylose to a hydroxylamino acid, mostcommonly serine or threonine, although 5-hydroxyproline or5-hydroxylysine may also be used.

Addition of glycosylation sites to the Apo-2 ligand polypeptide may beaccomplished by altering the amino acid sequence such that it containsone or more of the above-described tripeptide sequences (for N-linkedglycosylation sites). The alteration may also be made by the additionof, or substitution by, one or more serine or threonine residues to thenative Apo-2 ligand sequence (for O-linked glycosylation sites). TheApo-2 ligand amino acid sequence may optionally be altered throughchanges at the DNA level, particularly by mutating the DNA encoding theApo-2 ligand polypeptide at preselected bases such that codons aregenerated that will translate into the desired amino acids. The DNAmutation(s) may be made using methods described above and in U.S. Pat.No. 5,364,934, supra.

Another means of increasing the number of carbohydrate moieties on theApo-2 ligand polypeptide is by chemical or enzymatic coupling ofglycosides to the polypeptide. Depending on the coupling mode used, thesugar(s) may be attached to (a) arginine and histidine, (b) freecarboxyl groups, (c) free sulfhydryl groups such as those of cysteine,(d) free hydroxyl groups such as those of serine, threonine, orhydroxyproline, (e) aromatic residues such as those of phenylalanine,tyrosine, or tryptophan, or (f) the amide group of glutamine. Thesemethods are described in WO 87/05330 published 11 Sep. 1987, and inAplin and Wriston, CRC Crit. Rev. Biochem., pp. 259-306 (1981).

Removal of carbohydrate moieties present on the Apo-2 ligand polypeptidemay be accomplished chemically or enzymatically. For instance, chemicaldeglycosylation by exposing the polypeptide to the compoundtrifluoromethanesulfonic acid, or an equivalent compound can result inthe cleavage of most or all sugars except the linking sugar(N-acetylglucosamine or N-acetylgalactosamine), while leaving thepolypeptide intact. Chemical deglycosylation is described by Hakimuddin,et al., Arch. Biochem. Biophys., 259:52 (1987) and by Edge et al., Anal.Biochem., 118:131 (1981). Enzymatic cleavage of carbohydrate moieties onpolypeptides can be achieved by the use of a variety of endo- andexo-glycosidases as described by Thotakura et al., Meth. Enzymol.,138:350 (1987).

Glycosylation at potential glycosylation sites may be prevented by theuse of the compound tunicamycin as described by Duskin et al., J. Biol.Chem., 257:3105 (1982). Tunicamycin blocks the formation ofprotein-N-glycoside linkages.

Another type of covalent modification of Apo-2 ligand comprises linkingthe Apo-2 ligand polypeptide to one of a variety of nonproteinaceouspolymers, e.g., polyethylene glycol, polypropylene glycol, orpolyoxyalkylenes, in the manner set forth in U.S. Pat. Nos. 4,640,835;4,496,689; 4,301,144; 4,670,417; 4,791,192 or 4,179,337.

8. Epitope-tagged Apo-2 Ligand

The present invention also provides chimeric polypeptides comprisingApo-2 ligand fused to another, heterologous polypeptide. In oneembodiment, the chimeric polypeptide comprises a fusion of the Apo-2ligand with a tag polypeptide which provides an epitope to which ananti-tag antibody can selectively bind. The epitope tag is generallyplaced at,the amino- or carboxyl- terminus of the Apo-2 ligand. Thepresence of such epitope-tagged forms of the Apo-2 ligand can bedetected using an antibody against the tag polypeptide. Also, provisionof the epitope tag enables the Apo-2 ligand to be readily purified byaffinity purification using an anti-tag antibody or another type ofaffinity matrix that binds to the epitope tag.

Various tag polypeptides and their respective antibodies are well knownin the art. Examples include the flu HA tag polypeptide and its antibody12CA5 [Field et al., Mol. Cell. Biol., 8:2159-2165 J1988)]; the c-myctag and the 8F9, 3C7, 6E10, G4, B7 and 9E10 antibodies thereto [Evan etal., Molecular and Cellular Biology, 5:3610-3616 (1985)]; and the HerpesSimplex virus glycoprotein D (gD) tag and its antibody [Paborsky et al.,Protein Engineering, 3(6):547-553 (1990)). Other tag polypeptidesinclude the Flag-peptide (Hopp et al., BioTechnology, 6:1204-1210(1988)]; the KT3 epitope peptide' [Martin et al., Science, 255:192-194(1992)]; an α-tubulin epitope peptide [Skinner et al., J. Biol. Chem.,266:15163-15166 (1991)]; and the T7 gene 10 protein peptide tag[Lutz-Freyermuth et al., Proc. Natl. Acad. Sci. USA, 87:6393-6397(1990)]. Once the tag. polypeptide has been selected, an antibodythereto can be generated using the techniques disclosed herein.

Generally, epitope-tagged Apo-2 ligand may be constructed and producedaccording to the methods described above for native and variant Apo-2ligand. Apo-2 ligand-tag polypeptide fusions are preferably constructedby fusing the cDNA sequence encoding the Apo-2 ligand portion in-frameto the tag polypeptide DNA sequence and expressing the resultant DNAfusion construct in appropriate host cells. Ordinarily, when preparingthe Apo-2 ligand-tag polypeptide chimeras of the present invention,nucleic acid encoding the Apo-2 ligand will be fused at its 3′ end tonucleic acid encoding the N-terminus of the tag polypeptide, however 5′fusions are also possible. Examples of epitope-tagged Apo-2 ligand aredescribed in further detail in Example 2 below.

Epitope-tagged Apo-2 ligand can be purified by affinity chromatographyusing the anti-tag antibody. The matrix to which the affinity antibodyis attached may include, for instance, agarose, controlled pore glass orpoly(styrenedivinyl)benzene). The epitope-tagged Apo-2 ligand can thenbe eluted from the affinity column using techniques known in the art.

B. Therapeutic Uses for Apo-2 Ligand

Apo-2 ligand, as disclosed in the present specification, can be employedtherapeutically to induce apoptosis in mammalian cells. Generally, themethods for inducing apoptosis in mammalian cells comprise exposing thecells to an effective amount of Apo-2 ligand. This can be accomplishedin vivo or ex vivo in accordance, for instance, with the methodsdescribed below and in the Examples. It is contemplated that the methodsfor inducing apoptosis can be employed in therapies for particularpathological conditions which are characterized by decreased levels ofapoptosis. Examples of such pathological conditions include autoimmunedisorders like lupus and immune-mediated glomerular nephritis; andcancer. Therapeutic application of Apo-2 ligand for the treatment ofcancer is described in detail below.

In the methods for treating cancer, Apo-2 ligand is administered to amammal diagnosed as having cancer. It is of course contemplated that theApo-2 ligand can be employed in combination with still other therapeuticcompositions and techniques, including other apoptosis-inducing agents,chemotherapy, radiation therapy, and surgery.

The Apo-2 ligand is preferably administered to the mammal in apharmaceutically-acceptable carrier. Suitable carriers and theirformulations are described in Remington's Pharmaceutical

Sciences, 16th ed., 1980, Mack Publishing Co., edited by Oslo et al.Typically, an appropriate amount of a pharmaceutically-acceptable saltis used in the formulation to render the formulation isotonic. Examplesof the pharmaceutically-acceptable carrier include saline, Ringer'ssolution and dextrose solution.

The pH of the solution is preferably from about 5 to about 8, and morepreferably from about 7.4 to about 7.8. It will be apparent to thosepersons skilled in the art that certain carriers may be more preferabledepending upon, for instance, the route of administration andconcentration of Apo-2 ligand being administered.

The Apo-2 ligand can be administered to the mammal by injection (e.g.,intravenous, intraperitoneal, subcutaneous, intramuscular), or by othermethods such as infusion that ensure its delivery to the bloodstream inan effective form. It is also contemplated that the Apo-2 ligand can beadministered by in vivo or ex vivo gene therapy.

Effective dosages and schedules for administering Apo-2 ligand may bedetermined empirically, and making such determinations is within theskill in the art. It is presently believed that an effective dosage oramount of Apo-2 ligand used alone may range from about 1 pg/kg to about100 mg/kg of body weight or more per day. Interspecies scaling ofdosages can be performed in a manner. known in the art, e.q., asdisclosed in Mordenti et al., Pharmaceut. Res., 8:1351 (1991). Thoseskilled in the art will understand that the dosage of Apo-2 ligand thatmust be administered will vary depending on, for example, the mammalwhich will receive the Apo-2 ligand, the route of administration, andother drugs or therapies being administered to the mammal. The one ormore other therapies administered to the mammal may include but are notlimited to, chemotherapy and radiation therapy, immunoadjuvants,cytokines, and antibody-based therapies. Examples interleukins (e.g.,IL-1, IL-2, IL-3, IL-6), leukemia inhibitory factor, interferons,TGF-beta, erythropoietin, thrombopoietin, and HER-2 antibody. Otheragents known to induce apoptosis in mammalian cells may also employed,and such agents include TNF-α, TNF-β (lymphotoxin-a), CD30 ligand, 4-1BBligand, and Apo-1 ligand.

Chemotherapies contemplated by the invention include chemical substancesor drugs which are known in the art and are commercially available, suchas Doxorubicin, 5-Fluorouracil, Cytosine arabinoside (“Ara-C”),Cyclophosphamide, Thiotepa, Busulfan, Cytoxin, Taxol, Methotrexate,Cisplatin, Melphalan, Vinblastine and Carboplatin. Preparation anddosing schedules for such chemotherapy may be used according tomanufacturers' instructions or as determined empirically by the skilledpractitioner. Preparation and dosing schedules for such chemotherapy arealso described in Chemotherapy Service Ed., M. C. Perry, Williams &Wilkins, Baltimore, Md. (1992).

The chemotherapy is preferably administered in apharmaceutically-acceptable carrier, such as those described above forApo-2 ligand. The mode of administration of the chemotherapy may be thesame as employed for the Apo-2 ligand or it may be administered to themammal via a different mode. For example, the Apo-2 ligand may beinjected while the chemotherapy is administered orally to the mammal.

Radiation therapy can be administered to the mammal according toprotocols commonly employed in the art and known to the skilled artisan.Such therapy may include cesium, iridium, iodine, or cobalt radiation.The radiation therapy may be whole body irradiation, or may be directedlocally to a specific site or tissue in or on the body. Typically,radiation therapy is administered in pulses over a period of time fromabout 1 to about 2 weeks. The radiation therapy may, however, beadministered over longer periods of time. Optionally, the radiationtherapy may be administered as a single dose or as multiple, sequentialdoses.

The Apo-2 ligand and one or more other therapies may be administered tothe mammal concurrently or sequentially.

Following administration of Apo-2 ligand and one or more other therapiesto the mammal, the mammal's cancer and physiological condition can bemonitored in various ways well known to the skilled practitioner. Forinstance, tumor mass may be observed physically, by biopsy or bystandard x-ray imaging techniques.

It is contemplated that Apo-2 ligand can be employed to treat cancercells ex vivo. Such ex vivo treatment may be useful in bone marrowtransplantation and particularly, autologous bone marrowtransplantation. For instance, treatment of cells or tissue(s)containing cancer cells with Apo-2 ligand, and optionally, with one ormore other therapies, such as described above, can be employed to induceapoptosis and substantially deplete the cancer cells prior totransplantation in a recipient mammal.

Cells or tissue(s) containing cancer cells are first obtained from adonor mammal. The cells or tissue(s) may be obtained surgically andpreferably, are obtained aseptically. In the method of treating bonemarrow for transplantation, bone marrow is obtained from the mammal byneedle aspiration. The cells or tissue(s) containing cancer cells arethen treated with Apo-2 ligand, and optionally, with one or more othertherapies, such as described above. Bone marrow is preferablyfractionated to obtain a mononuclear cell fraction (such as bycentrifugation over ficoll-hypaque gradient) prior to treatment withApo-2 ligand.

The treated cells or tissue(s) can then be infused or transplanted intoa recipient mammal. The recipient mammal may be the same individual asthe donor mammal or may be another, heterologous mammal. For anautologous bone marrow transplant, the mammal is treated prior to thetransplant with an effective dose of radiation or chemotherapy as knownin the art and described for example in Autoloqous Bone MarrowTransplantation: Proceedings of the Third International Symposium, Dickeet al., eds., University of Texas M.D. Anderson Hospital and TumorInstitute (1987).

C. Non-Therapeutic Uses for Apo-2 Ligand

The Apo-2 ligand of the invention also has utility in non-therapeuticapplications. Nucleic acid sequences encoding the Apo-2 ligand may beused as a diagnostic for tissue-specific typing. For example, procedureslike in situ hybridization,

Northern and Southern blotting, and PCR analysis may be used todetermine whether DNA and/or RNA encoding Apo-2 ligand is present in thecell type(s) being evaluated. Apo-2 ligand nucleic acid will also beuseful for the preparation of Apo-2 polypeptide by the recombinanttechniques described herein.

The isolated Apo-2 ligand may be used in quantitative diagnostic assaysas a control against which samples containing unknown quantities ofApo-2 ligand may be prepared. Apo-2 ligand preparations are also usefulin generating antibodies, as standards in assays for Apo-2 ligand (e.g.,by labeling Apo-2 ligand for use as a standard in a radioimmunoassay,radioreceptor assay, or enzyme-linked immunoassay), in affinitypurification techniques for example, in identifying or in isolating areceptor that binds Apo-2 ligand, and in competitive-type receptorbinding assays when labeled with, for instance, radioiodine, enzymes, orfluorophores.

D. Anti-Apo-2 Ligand Antibody Preparation

The present invention .further provides anti-Apo-2 antibodies.Antibodies against Apo-2 ligand may be prepared as follows. Exemplaryantibodies include polyclonal, monoclonal, humanized, bispecific, andheteroconjugate antibodies.

1. Polyclonal Antibodies

The Apo-2 ligand antibodies may comprise polyclonal antibodies. Methodsof preparing polyclonal antibodies are known to the skilled artisan.Polyclonal antibodies can be raised in a mammal, for example, by one ormore injections of an immunizing agent and, if desired, an adjuvant.Typically, the immunizing agent and/or adjuvant will be injected in themammal by multiple subcutaneous or intraperitoneal injections. Theimmunizing agent may include the Apo-2 ligand polypeptide or a fusionprotein thereof. It may be useful to conjugate the immunizing agent to aprotein known to be immunogenic in the mammal being immunized. Examplesof such immunogenic proteins which may be employed include but are notlimited to keyhole limpet hemocyanin, serum albumin, bovinethyroglobulin, and soybean trypsin inhibitor. An aggregating agent suchas alum may also be employed to enhance the mammal's immune response.Examples of adjuvants which may be employed include Freund's completeadjuvant and MPL-TDM adjuvant (monophosphoryl Lipid A, synthetictrehalose dicorynomycolate). The immunization protocol may be selectedby one skilled in the art without undue experimentation. The mammal canthen be bled, and the serum assayed for antibody titer. If desired, themammal can be boosted until the antibody titer increases or plateaus. 2.Monoclonal Antibodies

The Apo-2 ligand antibodies may, alternatively, be monoclonalantibodies. Monoclonal antibodies may be prepared using hybridomamethods, such as those described by Kohler and Milstein, Nature, 256:495(1975). In a hybridoma method, a mouse, hamster, or other appropriatehost animal, is typically immunized (such as described above) with animmunizing agent to elicit lymphocytes that produce or are capable ofproducing antibodies that will specifically bind to the immunizingagent,. Alternatively, the lymphocytes may be immunized in vitro.

The immunizing agent will typically include the Apo-2 ligand polypeptideor a fusion protein thereof. Cells expressing Apo-2 ligand at theirsurface may also be employed. Generally, either peripheral bloodlymphocytes (“PBLs”) are used if cells of human origin are desired, orspleen cells or lymph node cells are used if non-human mammalian sourcesare desired. The lymphocytes are then fused with an immortalized cellline using a suitable fusing agent, such as polyethylene glycol, to forma hybridoma cell [Goding, Monoclonal Antibodies: Principles andPractice, Academic Press, (1986) pp. 59-103]. Immortalized cell linesare usually transformed mammalian cells, particularly myeloma cells ofrodent, bovine and human origin. Usually, rat or mouse myeloma celllines are employed. The hybridoma cells may be cultured in a suitableculture medium that preferably contains one or more substances thatinhibit the growth or survival of the unfused, immortalized cells. Forexample, if the parental cells lack the enzyme hypoxanthine guaninephosphoribosyl transferase (HGPRT or HPRT), the culture medium for thehybridomas typically will include hypoxanthine, aminopterin, andthymidine (“HAT medium”), which substances prevent the growth ofHGPRT-deficient cells.

Preferred immortalized cell lines are those that fuse efficiently,support stable high level expression of antibody by the selectedantibody-producing cells, and are sensitive to a medium such as HATmedium. More preferred immortalized cell lines are murine myeloma lines,which can be obtained, for instance, from the Salk Institute CellDistribution Center, San Diego, Calif. and the American Type CultureCollection, Rockville, Maryland. Human myeloma and mouse-humanheteromyeloma cell lines also have been described for the production ofhuman monoclonal antibodies [Kozbor, J. Immunol., 133:3001 (1984);Brodeur et al., Monoclonal Antibody Production Techniques andApplications, Marcel Dekker, Inc., New York, (1987) pp. 51-63].

The culture medium in which the hybridoma cells are cultured can then beassayed for the presence of monoclonal antibodies directed against Apo-2ligand. Preferably, the binding specificity of monoclonal antibodiesproduced by the hybridoma cells is determined by immunoprecipitation orby an in vitro binding assay, such ‘as radioimmunoassay (RIA) orenzyme-linked immunoabsorbent assay (ELISA). Such techniques and assaysare known in the art, and are described further in the Examples below.The binding affinity of the monoclonal antibody can, for example, bedetermined by the Scatchard analysis of Munson and Pollard, Anal.Biochem., 107:220 (1980).

After the desired hybridoma cells are identified, the clones may besubcloned by limiting dilution procedures and grown by standard methods[Goding, supra]. Suitable culture media for this purpose include, forexample, Dulbecco's Modified Eagle's Medium and RPMI-1640 medium.Alternatively, the hybridoma cells may be grown in vivo as ascites in amammal.

The monoclonal antibodies secreted by the subclones may be isolated orpurified from the culture medium or ascites fluid by conventionalimmunoglobulin purification procedures such as, for example, proteinA-Sepharose, hydroxylapatite chromatography, gel electrophoresis,dialysis, or affinity chromatography.

The monoclonal antibodies may also be made by recombinant DNA methods,such as those described in U.S. Pat. No. 4,816,567. DNA encoding themonoclonal antibodies of the invention can be readily isolated andsequenced using conventional procedures (e.g., by using oligonucleotideprobes that are capable of binding specifically to genes encoding theheavy and light chains of murine antibodies). The hybridoma cells of theinvention serve as a preferred source of such DNA. Once isolated, theDNA may be placed into expression vectors, which are then transfected.into host cells such as simian COS cells, Chinese hamster ovary (CHO)cells, or myeloma cells that did not otherwise produce immunoglobulinprotein, to obtain the synthesis of monoclonal antibodies in therecombinant host cells. The DNA also may be modified, for example, bysubstituting the coding sequence for human heavy and light chainconstant domains in place of the homologous murine sequences [U.S. Pat.No. 4,816,567; Morrison et al., supra] or by covalently joining to theimmunoglobulin coding sequence all or part of.the coding sequence for anon-immunoglobulin polypeptide. Such a non-immunoglobulin polypeptidecan be substituted for the constant domains of an antibody of theinvention, or can be substituted for the variable domains of oneantigen-combining site of an antibody of the invention to create achimeric bivalent antibody.

The antibodies may be monovalent antibodies. Methods for preparingmonovalent antibodies are well known in the art. For example, one methodinvolves recombinant expression of immunoglobulin light chain andmodified heavy chain. The heavy chain is truncated generally at anypoint in the Fc region so as to prevent heavy chain crosslinking.Alternatively,. the relevant cysteine residues are substituted withanother amino acid residue or are deleted so as to prevent crosslinking.

In vitro methods are also suitable for preparing monovalent antibodies.Digestion of antibodies to produce fragments thereof, particularly, Fabfragments, can be accomplished using routine techniques known in theart. For instance, digestion can be performed using papain. Examples ofpapain digestion are described in WO 94/29348 published Ser. No.12/22/94 and U.S. Pat. No. 4,342,566. Papain digestion of antibodiestypically produdes two identical antigen binding fragments, called Fabfragments, each with a single antigen binding site, and a residual Fcfragment. Pepsin treatment yields an F(ab′)₂ fragment that has twoantigen combining sites and is still capable of cross-linking antigen.

The Fab fragments produced in the antibody digestion also contain theconstant domains of the light chain and the first constant domain (CH₁)of the heavy chain. Fab′ fragments differ from Fab fragments by theaddition of a few residues at the carboxy terminus of the heavy chainCH₁ domain including one or more cysteines from the antibody hingeregion. Fab′-SH is the designation herein for Fab′ in which the cysteineresidue(s) of the constant domains bear a free thiol group. F(ab′)₂antibody fragments originally were produced as pairs of Fab′ fragmentswhich have hinge cysteines between them. Other chemical couplings ofantibody fragments are also known.

3. Humanized Antibodies

The Apo-2 ligand antibodies of the invention may further comprisehumanized antibodies or human antibodies. Humanized forms of non-human(e.g., murine) antibodies are chimeric immunoglobulins, immunoglobulinchains or fragments thereof (such as Fv, Fab, Fab′, F(ab′)₂ or otherantigen-binding subsequences of antibodies) which contain minimalsequence derived from non-human immunoglobulin. Humanized antibodiesinclude human immunoglobulins (recipient antibody) in which residuesfrom a complementary determining region (CDR) of the recipient arereplaced by residues from a CDR of a non-human species (donor antibody)such as mouse, rat or rabbit having the desired specificity, affinityand capacity. In some instances, Fv framework residues of the humanimmunoglobulin are replaced by corresponding non-human residues.Humanized antibodies may also comprise residues which are found neitherin the recipient antibody nor in the imported CDR or frameworksequences. In general, the humanized antibody will comprisesubstantially all of at least one, and typically two, variable domains,in which all or substantially all of the CDR regions correspond to thoseof a non-human immunoglobulin and all or substantially all of the FRregions are those of a human immunoglobulin consensus sequence. Thehumanized antibody optimally also will comprise at least a portion of animmunoglobulin constant region (Fc), typically that of a humanimmunoglobulin [Jones et al., Nature, 321:522-525 (1986); Reichmann etal., Nature, 332:323-329 (1988); and Presta, Curr. Op. Struct. Biol.,2:593-596 (1992)].

Methods for humanizing non-human antibodies are well known in the art.Generally, a humanized antibody has one or more amino acid residuesintroduced into it from a source which is non-human. These non-humanamino acid residues are often referred to as “import” residues, whichare typically taken from an “import” variable domain. Humanization canbe essentially performed following the method of Winter and co-workers[Jones et al., Nature, 321:522-525 (1986); Riechmann et al., Nature,332:323-327 (1988); Verhoeyen et al., Science, 239:1534-1536 (1988)], bysubstituting rodent CDRs or CDR sequences for the correspondingsequences of a human antibody. Accordingly, such “humanized” antibodiesare chimeric antibodies (U.S. Pat. No. 4,816,567), wherein substantiallyless than an intact human variable domain has been substituted by thecorresponding sequence from a non-human species. In practice, humanizedantibodies are typically human antibodies in which some CDR residues andpossibly some FR residues are substituted by residues from analogoussites in rodent antibodies.

The choice of human variable domains, both light and heavy, to be usedin making the humanized antibodies is very important in order to reduceantigenicity. According to the “best-fit” method, the sequence of thevariable domain of a rodent antibody is screened against the entirelibrary of known human variable domain sequences. The human sequencewhich is closest to that of the rodent is then accepted as the humanframework (FR) for the humanized antibody [Sims et al., J. Immunol.,151:2296 (1993); Chothia and Lesk, J. Mol. Biol., 196:901 (1987)].Another method uses a particular framework derived from the consensussequence of all human antibodies of a particular subgroup of light orheavy chains. The same framework may be used for several differenthumanized antibodies [Carter et al., Proc. Natl. Acad. Sci. USA, 89:4285(1992); Presta et al., J. Immunol., 151:2623 (1993)].

It is further important that antibodies be humanized with retention ofhigh affinity for the antigen and other favorable biological properties.To achieve this goal, according to a preferred method, humanizedantibodies are prepared by a process of analysis of the parentalsequences and various conceptual humanized products using threedimensional models of the parental and humanized sequences. Threedimensional immunoglobulin models are commonly available and arefamiliar to those skilled in the art. Computer programs are, availablewhich illustrate and display probable three-dimensional conformationalstructures of selected candidate immunoglobulin sequences. Inspection ofthese displays permits analysis of the likely role of the residues inthe functioning, of the candidate immunoglobulin sequence, i.e., theanalysis.of residues that influence the ability of the candidateimmunoglobulin to bind its antigen. In this way, FR residues can beselected and combined from the consensus and import sequence so that thedesired antibody characteristic, such as increased affinity for thetarget antigen(s), is achieved. In general, the CDR residues aredirectly and most substantially involved in influencing antigen binding[see, WO 94/04679 published 3 Mar. 1994].

Transgenic animals (e.g., mice) that are capable, upon immunization, ofproducing a full repertoire of human antibodies in the absence ofendogenous immunoglobulin production can be employed. For example, ithas been described that the homozygous deletion of the antibody heavychain joining region (J_(H)) gene in chimeric and germ-line mutant miceresults in complete inhibition of endogenous antibody production.Transfer of the human germ-line immunoglobulin gene array in suchgerm-line mutant mice will result in the production of human antibodiesupon antigen challenge [see, e.g., Jakobovits et al., Proc. Natl. Acad.Sci. USA, 90:2551-255 (1993); Jakobovits et al., Nature, 362:255-258(1993); Bruggermann et al., Year in Immuno., 7:33 (1993)]. Humanantibodies can also be produced in phage display libraries [Hoogenboomand Winter, J. Mol. Biol., 227:381 (1991); Marks et al., J. Mol. Biol.,222:581 (1991)]. The techniques of Cote et al. and Boerner et al. arealso available for the preparation of human monoclonal antibodies (Coteet al., Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, p. 77(1985) and Boerner et al., J. Immunol., 147(1):86-95 (1991)].

4. Bispecific Antibodies

Bispecific antibodies,are monoclonal, preferably human or humanized,antibodies that have binding specificities for at least two differentantigens. ‘In the present case, one of the binding specificities is forthe Apo-2 ligand, the other one is for any other antigen, and preferablyfor a cell-surface protein or receptor or receptor subunit.

Methods for making bispecific antibodies-are known in the art.Traditionally, the recombinant production of bispecific antibodies isbased on the co-expression of two immunoglobulin heavy-chain/light-chainpairs, where the two heavy chains have different specificities[Millstein and Cuello, Nature, 305:537-539 (1983)]. Because of therandom assortment of immunoglobulin heavy and light chains, thesehybridomas (quadromas) produce a potential mixture of ten differentantibody molecules, of which only one has the correct bispecificstructure. The purification of the correct molecule is usuallyaccomplished by affinity chromatography steps. Similar procedures aredisclosed in WO 93/08829, published 13 May 1993, and in Traunecker etal., EMBO J., 10:3655-3659 (1991).

According to a different and more preferred approach, antibody variabledomains with the desired binding specificities (antibody-antigencombining sites) are fused to immunoglobulin constant domain sequences.The fusion preferably is with an immunoglobulin heavy-chain constantdomain, comprising at least part of the hinge, CH2, and CH3 regions. Itis preferred to have the first heavy-chain constant region (CH1)containing the site necessary for light-chain binding present in atleast one of the fusions. DNAs encoding the immunoglobulin heavy-chainfusions and, if desired, the immunoglobulin light chain, are insertedinto separate expression vectors, and are co-transfected into a suitablehost organism. This provides for great flexibility in adjusting themutual proportions of the three polypeptide fragments in embodimentswhen unequal ratios of the three polypeptide chains used in theconstruction provide the optimum yields. It is, however, possible toinsert the coding sequences for two or all three polypeptide chains inone expression vector when the expression of at least two polypeptidechains in equal ratios results in high yields or when the ratios are ofno particular significance. In a preferred embodiment of this approach,the bispecific antibodies are composed of a hybrid immunoglobulin heavychain with a first binding specificity in one arm, and a hybridimmunoglobulin heavy-chain/light-chain pair (providing a second bindingspecificity) in the other arm. It was found that this asymmetricstructure facilitates the separation of the desired bispecific compoundfrom unwanted immunoglobulin chain combinations, as the presence of animmunoglobulin light chain in only one half of the bispecific moleculeprovides for a facile way of separation. This approach is disclosed inWO 94/04690 published March 1994. For further details of generatingbispecific antibodies see, for example, Suresh et al., Methods inEnzymology, 121:210 (1986).

5. Heteroconjugate Antibodies

Heteroconjugate antibodies are also within the scope of the presentinvention. Heteroconjugate antibodies are composed of two covalentlyjoined antibodies. Such antibodies have, for example, been proposed totarget immune system cells to unwanted cells [U.S. Pat. No. 4,676,980],and for treatment of HIV infection [WO 91/00360; WO 92/200373; EP03089]. It is contemplated that the antibodies may be prepared in vitrousing known methods in synthetic protein chemistry, including thoseinvolving crosslinking agents. For example, immunotoxins may beconstructed using a disulfide exchange reaction or by forming athioether bond. Examples of suitable reagents for this purpose includeiminothiolate and methyl-4-mercaptobutyrimidate and those disclosed, forexample, in U.S. Pat. No. 4,676,980.

E. Uses of Apo-2 Ligand Antibodies

Apo-2 ligand antibodies may be used in diagnostic assays for Apo-2ligand, e.g., detecting its expression in specific cells, tissues, orserum. Various diagnostic assay techniques known in the art may be used,such as competitive binding assays, direct or indirect sandwich assaysand immunoprecipitation assays conducted in either heterogeneous orhomogeneous phases [Zola, Monoclonal Antibodies: A Manual of Techniques,CRC Press, Inc. (1987) pp. 147-158]. The antibodies used in thediagnostic assays can be labeled with a detectable moiety. Thedetectable moiety should be capable of producing, either directly orindirectly, a detectable signal. For example, the detectable moiety maybe a radioisotope, such as ³H, ¹⁴C, ³⁵S, or ¹²⁵I, a fluorescent orchemiluminescent compound, such as fluorescein isothiocyanate,rhodamine, or luciferin, or an enzyme, such as alkaline phosphatase,beta-galactosidase or horseradish peroxidase. Any method known in theart for conjugating the antibody to the detectable moiety may beemployed, including those methods described by Hunter et al., Nature,144:945 (1962); David et al., Biochemistry, 13:1014 (1974); Pain et al:,J. Immunol. Meth., 40:219 (1981); and Nygren, J. Histochem. andCytochem., 30:407 (1982).

Apo-2 ligand antibodies also are useful for the affinity purification ofApo-2 ligand from recombinant cell culture or natural sources. In thisprocess, the antibodies against Apo-2 ligand are immobilized on asuitable support, such a Sephadex resin or filter paper, using methodswell known in the art. The immobilized antibody then is contacted with asample containing the Apo-2 ligand to be purified, and thereafter thesupport is washed with a suitable solvent that will remove substantiallyall the material in the sample except the Apo-2 ligand, which is boundto the immobilized antibody. Finally, the support is washed with anothersuitable solvent that will release the Apo-2 ligand from the antibody.Apo-2 ligand antibodies also are useful for the affinity purification ofa solubilized Apo-2 receptor or. for expression cloning of .an Apo-2receptor.

F. Kits Containing Apo-2 Ligand or Apo-2 Ligand Antibodies

In a further embodiment of the invention, there are provided articles ofmanufacture and kits containing Apo-2 ligand or Apo-2 ligand antibodieswhich can be used, for instance, for the therapeutic or non-therapeuticapplications described above. The article of manufacture comprises acontainer with a label. Suitable containers include, for example,bottles, vials, and test tubes. The containers may be formed from avariety of materials such as glass or plastic. The container holds acomposition which includes an active agent that is effective fortherapeutic or non-therapeutic applications, such as-described above.The active agent in the composition is Apo-2 ligand or an Apo-2 ligandantibody. The label on the container indicates that the composition isused for a specific therapy or non-therapeutic application, and may alsoindicate directions for either in vivo or in vitro use, such as thosedescribed above.

The kit of the invention will typically comprise the container describedabove and one or more other containers comprising materials desirablefrom a commercial and user standpoint, including buffers, diluents,filters, needles, syringes, and package inserts with instructions foruse. *****************************

The following examples are offered for illustrative purposes only, andare not intended to limit the scope of the present invention in any way.

All references cited in the present specification are herebyincorporated by reference in their entirety.

EXAMPLES

All restriction enzymes referred to in the examples were purchased fromNew England Biolabs and used according to manufacturer's instructions.All other commercially available reagents referred to in the exampleswere used according to manufacturer's instructions unless otherwiseindicated. The source of those cells identified in the followingexamples, and throughout the specification, by ATCC accession numbers isthe American Type Culture Collection, Rockville; Md.

Example 1

Isolation of cDNA Clones Encoding Human Apo-2 Ligand

To isolate a full-length cDNA for Apo-2 ligand, a lambda gtllbacteriophage library of human placental cDNA (about 1×10⁶ clones)(HL10756, commercially available from Clontech) was screened byhybridization with synthetic oligonucleotide probes based on an ESTsequence (GenBank locus HHEA47M), which showed some degree of homologyto humanTas/Apo-1 ligand. The EST sequence of HHEA47M is 390 by and whentranslated in its +3 frame, shows 16 identities to a 34 amino acidregion of human Apo-1 ligand. The sequence of HHEA47M is as follows:

SEQ ID NO: 3 GGGACCCCAATGACGAAGAGAGTATGAACAGCCCCTGCTGGCAAGTCAAGTGGCAACTCCGTCAGCTCGTTAGAAAGATGATTTTGAGAACCTCTGAGGAAACCATTTCTACAGTTCAAGAAAAGCAACAAAATATTTCTCCCCTAGTGAGAGAAAGAGGTCCTCAGAGAGTAGCAGCTCACATAACTGGGACCAGAGGAAGAAGCAACACATTGTCTTCTCCAAACTCCAAGAATGAAAAGGCTCTGGGCCGCAAAATAAACTCCTGGGAATCATCAAGGAGTGGGCATTCATTCCTGAGCAACTTGCACTTGAGGAATGGTGAACTGGTCATCCATGAAAAAGGGTTTTACTACATCTATTCCCAAACATACTTTCGATTTCAGGAGG

A 60 by oligonucleotide probe with the following sequence was employed in t h e screening:

SEQ ID NO: 4 TGACGAAGAGAGTATGAACAGCCCCTGCTGGCAAGTCAAGTGGCAACTCCGTCAGCTCGT

Hybridization was conducted overnight at room temperature in buffercontaining 20% formamide, 5×SSC, 10% dextran sulfate, 0.1% NaPiPO₄,0.05M NaPO₄, 0.05 mg salmon sperm DNA, and 0.1% sodium dodecyl sulfate,followed by several washes at 42° C. in 5×SSC, and then in 2×SSC. Twelvepositive clones were identified in the cDNA library, and the positiveclones were rescreened by hybridization to a second 60 byoligonucleotide probe (not overlapping the first probe) having thefollowing sequence:

SEQ ID NO: 5 GGTGAACTGGTCATCCATGAAAAAGGGTTTTACTACATCTATTCCCAAACATACTTTCGAHybridization was conducted as described above.

Four resulting positive clones were identified and amplified bypolymerase chain reaction (PCR) using a primer based on the flanking 5′vector sequence and adding an external ClaI restriction site and aprimer based on the 3′ flanking vector sequence acid adding an externalHindIII restriction site. PCR products were gel purified and subclonedinto pGEM-T (commercially available from Promega) by T-A ligation. Threeindependent clones from different PCRs were then subjected to dideoxyDNA sequencing. DNA sequence analysis of these clones demonstrated thatthey were essentially identical, with some length variation at their 5′region.

The nucleotide sequence of the coding region of Apo-2 ligand is shown inFIG. 1A. Sequencing of the downstream 3′ end region of one of the clonesrevealed a characteristic polyadenylation site (data not shown). ThecDNA contained one long open reading frame with an initiation siteassigned to the ATG codon at. nucleotide positions 91-93. Thesurrounding sequence at this site is in reasonable agreement with theproposed consensus sequence for initiation sites [Kozak, J. Cell. Biol.,115:887-903 (1991)]. The open reading frame ends at the terminationcodon TAA at nucleotide positions 934-936.

The predicted mature amino acid sequence of human Apo-2 ligand contains281 amino acids, and has a calculated molecular weight of approximately32.5 kDa and an isoelectric point of approximately 7.63. There is noapparent signal sequence at the N-terminus, although hydropathy analysis(data not shown) indicated the presence of a hydrophobic region betweenresidues 15 and 40. The absence of a signal sequence and the presence ofan internal hydrophobic region suggests that Apo-2 ligand is a type IItransmembrane protein. The putative cytoplasmic, transmembrane andextracellular regions are 14, 26 and 241 amino acids long, respectively.The putative transmembrane region is underlined in FIG. 1A. A potentialN-linked glycosylation site is located at residue 109 in the putativeextracellular domain.

An alignment (using the Align' computer program) of the amino acidsequence of the C-terminal region of Apo-2 ligand with other knownmembers of the TNF cytokine family showed that, within the C-terminalregion, Apo-2 ligand exhibits 23.2% identity to Apo-1 ligand (FIG. 1B).The alignment analysis showed a lesser degree of identity with other TNFfamily members: CD40L (20.8%), LT-α (20.2%), LT-β (19.6%), TNF-α(19.0%), ‘CD30L and CD27L (15.5%), OX-40L (14.3%), and 4-1BBL (13.7%).In the TNF cytokine family, residues within regions which are predictedto form β strands, based on the crystal structures of TNF-α and LT-α[Eck et al., J. Bio. Chem., 264:17595-17605 (1989); Eck et al., J. Bio.Chem., 267:2119-2122 (1992)], tend to be more highly conserved withother TNF family members than are residues in the predicted connectingloops. It was found that Apo-2 ligand exhibits greater homology to otherTNF family members in its putative β strand regions, as compared tohomology in the predicted connecting loops. Also, the loop connectingputative β strands, B and B’, is markedly longer in Apo-2 ligand.

Example 2 Expression of Human Apo-2 Ligand

A. Full-length cDNA Fusion Construct

A full-length Apo-2 ligand cDNA fused to a myc epitope tag wasconstructed as follows. The Apo-2 ligand cDNA insert was excised fromthe parental pGEM-T Apo-2 ligand plasmid (described in Example 1) bydigestion with ClaI and HindIII, and inserted into a pRK5 mammalianexpression plasmid [Schall et al., Cell, 61:361-370 (1990); Suva et al.,Science, 237:893-896 (1987)], which was digested with the samerestriction enzymes. A sequence encoding a 13 amino acid myc epitope tagSer Met Glu Gln Lys Leu Ile Ser Glu Glu Asp Leu Asn SEQ ID NO:6 [Evan etal., Mol. Cell. Biol., 5:3610-3616 (1985)] was then inserted betweencodon 281 and the stop codon (codon 282) at the 3′ end of the Apo-2ligand coding sequence by oligonucleotide directed mutagenesis [Zolleret al., Nucleic Acids Res., 10:6487-6496 (1982)] to give plasmid pRK5Apo-2 ligand-myc.

The pRK5 Apo-2 ligand-myc plasmid was co-transfected into human 293cells (ATCC CRL 1573) with a pRK5 plasmid carrying a neomycin resistancegene, by calcium phosphate precipitation. Stable clones expressing Apo-2ligand-myc were selected by ability to grow in 50% HAM's F12/50% DMEM(GIBCO) media in the presence of the antibiotic, G418 (0.5 mg/mL)(GIBCO).

To investigate the topology of Apo-2 ligand, a G418-resistant clone wasanalyzed by FACS after staining with anti-myc monoclonal antibody, (mAb)clone 9E10 [Evan et al., supra; commercially available from OncogeneScience) followed by a phycoerythrin (PE)-conjugated goatanti-mouse-antibody (commercially available from JacksonImmunoResearch). The FACS analysis revealed a specific positive stainingshift in the Apo-2 ligand-myc-transfected clone as compared to mocktransfected cells (FIG. 1C), showing that Apo-2 ligand is expressed atthe cell-surface, with its carboxy terminus exposed. Accordingly, Apo-2ligand is believed to be a type II transmembrane protein.

B. ECD Fusion Constructs

Two soluble Apo-2 ligand extracellular domain (“ECD”) fusion constructswere prepared, in which another sequence was fused upstream of theC-terminal region of Apo-2 ligand. In one construct, 27 amino acids ofthe herpes virus glycoprotein D (“gD”) signal peptide [described inLasky et al., DNA, 3:23-29 (1984); Pennica et al., Proc. Natl. Acad.Sci., 92:1142-1146 (1995); Paborsky et al., Protein Engineering,3:547-553 (1990)] and epitope tag sequence

SEQ ID NO: 7 Lys Tyr Ala Leu Ala Asp Ala Ser Leu Lys Met AlaAsp Pro Asn Arg Phe Arg Gly Lys Asp Leu Pro Val Leu Asp Glnwere fused upstream to codons 114-281 of Apo-2 ligand within a pRK5mammalian expression plasmid. Briefly, the gD sequence was amplifiedfrom a parent plasmid, pCHAD (Genentech, prepared substantially asdescribed in Lasky et al., Science, 233:209-212 (1986)), in a PCR inwhich the 3′ primer was complementary to the 3′ region of the gDsequence as well as to codons 114-121 of Apo-2 ligand. The product wasused as a 5′ primer along with a 3′ primer complementary to the 3′ endof the Apo-2 ligand-coding region in a subsequent PCR in which the pRK5Apo-2 ligand plasmid was'used as a template. The product, encoding thegD-Apo-2 ligand ECD fusion was then subcloned into a pRK5 plasmid togive the plasmid pRK5 gD-Apo-2 ligand ECD.

Human embryonic kidney 293 cells (ATCC CRL 1573) were transientlytransfected with the pRK5 gD-Apo-2 ligand ECD plasmid or with pRK5, bycalcium phosphate precipitation. Expression of soluble gD-Apo-2 ligandprotein was assessed by metabolic labeling of the transfected cells with³⁵S-Cys and ³⁵S-Met. Cell supernatants were collected after 24 hours andcleared by centrifugation. For immunoprecipitation, 5 ml of supernatantwere incubated with 5B6 anti-gD monoclonal antibody (Genentech) at 1μg/ml overnight at 4° C. Then, 25 μl Pansorbin (Sigma) was added foranother 1 hour at 4° C. The tubes were spun, the pellets were washed inPBS and boiled for 5 minutes in SDS sample buffer. The boiled sampleswere spun again, and the supernatants were subjected to SDS-PAGE andautoradiography.

Immunoprecipitation with anti-gD antibody revealed three predominantprotein bands in the supernatants of cells transfected with the gD-Apo-2ligand plasmid (FIG. 1E). These bands migrated with relative molecularmasses (Mr) of 23, 48 and 74 kDa. The calculated molecular weight of themature gD-Apo-2 polypeptide is approximately 22.5 kDa; hence, theobserved bands may represent monomeric (23 kDa), dimeric (48 kDa) andtrimeric (74 kDa) forms of the fusion protein, and indicate that Apo-2ligand can be expressed as a secreted soluble gD fusion protein inmammalian cells.,

In a second construct, a Met Gly His. sequence (derived from the plasmidpET19B, Novagen), followed by a 12 amino acid enterokinase cleavage siteMet Gly His His His His His His His His His His Ser Ser Gly His Ile AspAsp Asp Asp Lys His Met SEQ ID NO:8 was fused upstream to codons 114-281of Apo-2 ligand within a baculovirus expression plasmid (pVL1392,Pharmingen). Briefly, the Apo-2 ligand codon 114-281 region wasamplified by PCR from the parent pRK5 Apo-2 ligand plasmid (described inExample 1) with primers complementary to the 5′ and 3″ regions whichincorporate flanking NdeI and BamHI restriction sites respectively. Theproduct was subcloned into pGEM-T (Promega) by T-A ligation, and the DNAsequence was confirmed. The insert was then excised by digestion withNdeI and BamHI and subcloned into a modified baculovirus expressionvector pVL1392 (commercially available from Pharmingen) containing anamino terminal Met Gly His_(to) tag and enterokinase cleavage site.

Recombinant baculovirus was generated by co-transfecting the His₁₀-Apo-2ECD plasmid and BaculoGold™ virus DNA (Pharmingen) into Spodopterafrugiperda (“Sf9”) cells (ATCC CRL 1711) using lipofectin (commerciallyavailable from GIBCO-BRL). After 4-5 days of incubation at 28° C., thereleased viruses were harvested and used for further amplifications.Viral infection and protein expression was performed as described byO'Reilley et al., Baculovirus expression vectors: A laboratory Manual,Oxford:Oxford University Press (1994). The protein was purified byNi²⁺-chelate affinity chromatography, as described in Example 3 below.

Example 3 Purification of Recombinant Human Apo-2 Ligand

Extracts were prepared from recombinant virus-infected and mock-infectedSf9 cells (see Example 2, section B above) as described by Rupert etal., Nature, 362:175-179 (1993). Briefly, Sf9 cells were washed,resuspended in sonication buffer (25 mL Hepes, pH 7.9; 12.5 mM MgCl₂;0.1 mM EDTA; 10% Glycerol; 0.1% NP-40; 0.4 M KCl), and sonicated twicefor 20 seconds on ice. The sonicates were cleared by centrifugation, andthe supernatant was diluted 50-fold in loading buffer (50 mM phosphate,300 mM NaCl, 10% Glycerol, pH 7.8) and filtered through a 0.45 μmfilter. A Ni²⁺-NTA agarose column (commercially available from Qiagen)was prepared with a bed volume of 5 mL, washed with 25 mL of water andequilibrated with 25 mL of loading buffer. The filtered cell extract wasloaded onto the column at 0.5 mL per minute. The column was washed tobaseline A₂₈₀ with loading buffer, at which point fraction collectionwas started. Next, the column was washed with a secondary wash buffer(50 mM phosphate; 300 mM NaCl, 10% Glycerol, pH 6.0), which elutednonspecifically. bound protein. After reaching A₂₈₀ baseline again, thecolumn was developed with a 0 to 500 mM Imidazole gradient in thesecondary wash buffer. One mL fractions were collected and analyzed bySDS-PAGE and silver staining or western blot with Ni²⁺-NTA-conjugated toalkaline phosphatase (Qiagen). Fractions containing the elutedHis₁₀-Apo-2 ligand protein were pooled and dialyzed against loadingbuffer.

An identical procedure was repeated with mock-infected Sf9 cells as thestarting material, and the same fractions were pooled, dialyzed, andused as control for the purified human Apo-2.

SDS-PAGE analysis of the purified protein revealed a predominant band ofMr 24 kDa, corresponding with the calculated molecular weight of 22.4kDa for the His₁₀-Apo-2 ligand monomer (FIG. 1D, lane 3); proteinsequence microanalysis (data not shown) confirmed that the 24 kDa bandrepresent's the His₁₀-Apo-2 ligand polypeptide. Minor 48 kDa and 66 kDabands were also observed, and probably represent soluble Apo-2 ligandhomodimers and homotrimers. Chemical crosslinking of the purifiedHis₁₀-Apo-2 ligand by incubation with sulfo-NHS (5mM) (Pierce Chemical)and EDC (Pierce Chemical) at 25 mM and 50 mM (FIG. 1D, lanes 1 and 2,respectively), shifted the protein into the 66 kDa band primarily. Theseresults suggest that the predominant form of Apo-2 ligand in solution ishomotrimeric and that these trimers dissociate into dimers and monomersin the presence of SDS.

Example 4 Apoptotic Activity of Apo-2 Ligand on Human Lymphoid CellLines

Apoptotic activity of purified, soluble Apo-2 ligand (described inExample 3) was examined using several human lymphoid cell lines. In afirst study, the effect of Apo-2 ligand on 9D cells (Genentech, Inc.),derived from Epstein-Barr virus (EBV)-transformed human peripheral bloodB cells, was examined. The 9D cells (5×10⁴ cells/well in RPMI 1640medium plus 10% fetal calf serum) were incubated for 24 hours witheither a media control, Apo-2 ligand (3 μg/ml, prepared as described inExample 3 above), or anti-Apo-1 monoclonal antibody, CH11 (1 μg/ml)[described by Yonehara et al., J. Exp. Med., 169:1747-1756 (1989);commercially available from Medical and Biological Laboratories Co.].The CH11 anti-Apo-1 antibody is an agonistic antibody which mimicksFas/Apo-1 ligand activity.

After the incubation, the cells were collected onto cytospin glassslides, and photographed under an inverted light microscope. Both Apo-2ligand and the anti-Apo-1 monoclonal antibody induced a similarapoptotic effect, characterized by cytoplasmic condensation andreduction in cell numbers. (see FIG. 2A).

The effects of the Apo-2 ligand on the 9D cells, as well as on Rajicells (human Burkitt's lymphoma B cell line, ATCC CCL 86) and Jurkatcells (human acute T cell leukemia cell line, ATCC TIB 152) were furtheranalyzed by FACS. The FACS analysis was conducted, using establishedcriteria for apoptotic cell death, namely, the relation of fluorescencestaining of the cells with two markers: (a) propidium iodide (“PI”) dye,which stains apoptotic but not live cells, and (b) a fluorescentderivative of the protein, annexin V, which binds to the exposedphosphatidylserine found on the surface of apoptotic cells, but not onlive cells [Darzynkiewicz et al., Methods in Cell Biol., 41:15-38(1994); Fadok et al., J. Immunol., 148:2207-2214 (1992); Koopman et al.,Blood, 84:1415-1420 (1994)].

The 9D cells (FIG. 2B), Raji cells (FIG. 2C), and Jurkat cells (FIG. 2D)were incubated (1×10⁶ cells/well) for 24 hours with a media control(left panels), Apo-2 ligand (3 μg/ml, prepared as described in Example3) (center panels), or anti-Apo-1 ligand antibody, CH11 (1 μg/ml) (rightpanels). The cells were then washed, stained with PI and withfluorescein thiocyanate (FITC)-conjugated annexin V (purchased fromBrand Applications) and analyzed by flow cytometry. .Cells negative forboth PI and annexin V staining (quadrant 3) represent live cells;PI-negative, annexin V-positive staining cells (quadrant 4) representearly apoptotic cells; PI-positive, annexin V-positive staining cells(quadrant 2) represent primarily cells in late stages of apoptosis.

The Apo-2 ligand treated 9D cells exhibited elevated extracellularannexin V binding, as well as a marked increase in uptake of PI (FIG.2B), indicating that Apo-2 ligand induced apoptosis in the cells.Comparable results were obtained with anti-Apo-1 antibody, CH11 (FIG.2B). The Apo-2 ligand induced a similar response in the Raji and Jurkatcells, as did the anti-Apo-1 antibody. (see FIGS. 2C and 2D). Theinduction of apoptosis (measured as the % apoptotic cells) in these celllines by Apo-2 ligand, as compared to the control and to the anti-Apo-1antibody, is also shown in Table 1 below.

The activation of internucleosomal DNA fragmentation by Apo-2 ligand wasalso analyzed. Jurkat cells (left lanes) and 9D cells (right lanes) wereincubated (2×10⁶ cells/well) for 6 hours with a media control or Apo-2ligand (3 μg/ml, prepared as described in Example 3), The DNA was thenextracted from the cells and labeled with ³²P-ddATP using terminaltransferase. The labeled DNA samples were subjected to electrophoresison 2% agarose gels and later analyzed by autoradiography [Moore et al.,Cytotechnology, 17:1-11 (1995)]. The Apo-2 ligand inducedinternucleosomal DNA fragmentation in both the Jurkat cells and 9D cells(FIG. 2E). Such DNA fragmentation is characteristic of apoptosis [Cohen,Advances in Immunol., 50:55-85 (1991)].

To examine the time-course of the Apo-2 ligand apoptotic activity, 9Dcells were incubated in microtiter dishes (5×10⁴ cells/well) with amedia control or Apo-2 ligand (3 μg/ml, prepared as described in Example3) for a period of time ranging from 0 hours to 50 hours. Following theincubation, the numbers of dead and live cells were determined bymicroscopic examination using a hemocytometer.

As shown in FIG. 3A, maximal levels of cell death were induced in 9Dcells within 24 hours.

To determine dose-dependency of Apo-2 ligand-induced cell death, 9Dcells were incubated (5×10⁴ cells/well) for 24 hours with serialdilutions of a media control or Apo-2 ligand (prepared as described inExample 3). The numbers of dead and live cells following the incubationwere determined as described above. The results are illustrated in FIG.3B. Specific apoptosis was determined by subtracting the % apoptosis inthe control from % apoptosis in Apo-2 ligand treated cells. Half-maximalactivation of apoptosis occurred at approximately 0.1 μg/ml(approximately 1 nM), and maximal induction occurred at about 1 to about3 μg/ml (approximately 10 to 30 nM).

Example 5 Apoptotic Activity of Apo-2 Ligand on Human Non-Lymphoid TumorCell Lines

The effect of Apo-2 ligand on human non-lymphoid tumor cell lines wasexamined using the following cell lines: HeLa (derived from humancervical carcinoma, ATCC CCL 22); ME-180 (derived from human cervicalcarcinoma, ATCC HTB 33); MCF7 (derived from human breast carcinoma, ATCCHTB 22); U-937 (derived from human hystiocytic lymphoma, ATCC CRL 1593);A549 (derived from human lung carcinoma, ATCC CCL 185); and 293 (derivedfrom an adenovirus-transformed human embryonic kidney cells, ATCC CCL1573).

In the assay, 1×10⁶ cells of each cell line were incubated for 24 hourswith a media control, Apo-2 ligand (3 μg/ml, prepared as described inExample 3), or anti-Apo-1 monoclonal antibody, CH 11 (1 μg/ml).Following the incubation, apoptosis was measured by FACS analysis, asdescribed in Example 4. The results are shown below in Table 1.

TABLE 1 % apoptotic cells Cell line Control Apo-2L Anti-Apo-1 AbLymphoid 9D 22.5 92.4 90.8 Raji 35.9 73.4 83.7 Jurkat 5.9 77.0 18.1Non-lymphoid HeLa 5.3 18.6 17.9 MCF7 39.9 47.3 44.0 U-937 3.6 62.3 16.6A549 16.5 74.6 25.1 ME-180 8.6 80.7 9.9 293 12.3 12.2 16.7

The HeLa cells and MCF7 cells were equally sensitive to induction ofapoptosis by Apo-2 ligand as compared to the CH11 anti-Apo-1 antibody.In contrast, the U-937 cells and A549 cells were markedly more sensitiveto induction of apoptosis by Apo-2 ligand. The ME-180 cells were quitesensitive to the Apo-2 ligand, but were relatively resistant to theanti-apo-1 antibody. The 293 cells were resistant to the Apo-2 ligandand weakly responsive to the anti-Apo-1 antibody.

Thus, Apo-2 ligand is capable of inducing apoptosis in cells ofnon-lymphoid origin, as well as cells of lymphoid origin (see Example4). Also, although not fully understood and not wishing to be bound byany particular theory, Applicants presently believe that Apo-2 ligandacts via a receptor which is distinct from Apo-1. This belief issupported by the data herein showing that the cell lines described aboveexhibit differential patterns of sensitivity to Apo-2 ligand and toanti-Apo-1 antibody. (see also, Example 7 below).

Example 6 Effect of Apo-2 Ligand on Human Peripheral Blood Monocytes

Peripheral blood mononuclear cells (“PBMC”) were isolated from the bloodof human donors by Ficoll density gradient centrifugation using.Lymphocyte Separation Medium (LSM®, Organon Teknika). An isolatedpopulation of T cells was prepared from the PBMC by removal of B cellsthrough surface Ig binding to an anti-Ig column and removal of monocytesthrough Fc receptor binding to an Ig column (R & D Systems). An isolatedpopulation of B cells was prepared from the PBMC by complement-thediatedelimination of T cells reacted with the anti-CD3 antibody produced bythe OKT3 myeloma (ATCC, CRL 8001) and of monocytes reacted with amonocyte-specific antibody produced by the 4F2C13 hybridoma (ATCC, HB22). Additional monocyte removal was accomplished by adherence toplastic.

The freshly isolated peripheral blood B or T cells (1×10⁶ cells/well)were cultured for 3 days in the presence of a media control or Apo-2ligand (3 μg/ml, prepared as described in Example 3). For activation, Bcells were treated simultaneously with lipopolysaccharide (“LPS”, 1μg/ml), and T cells were treated with phorbol myristate acetate (“PMA”,10 ng/ml) plus ionomycin (1 μg/ml) (Sigma). For interleukin-2 (“IL-2”)pretreatment, T cells were cultured for 3-5 days in the presence of IL-2(50 U/ml) (Genzyme) before exposure to Apo-2 ligand. Apoptosis wasdetermined using FACS analysis essentially as described above in Example4. However, B cells were gated by anti-CD19/CD20 antibodies (JacksonImmunoresearch), and T cells were gated by anti-CD4/CD8 antibodies(Jackson Immunoresearch). The results are shown in Table 2 below,representing means±SE of independent experiments [B lymphocytes -9experiments; T lymphocytes -8 experiments; T lymphocytes plus IL-2-5experiments], in which 50,000 cells were analyzed per data point.Statistical analysis was performed using the student t-test. In Table 2,a=p<0.05 and b=p<0.02 relative to the respective control.

TABLE 2 % apoptotic cells Treatment Control Apo-2L B lymphocytes none40.1 ± 4.1 53.2 ± 3.3^(a) LPS 44.8 ± 2.8 55.9 ± 3.2^(a) T lymphocytesnone  6.3 ± 0.6  8.2 ± 0.8  PMA/ionomycin 40.3 ± 4.4 54.2 ± 3.3^(a) IL-213.7 ± 1.2 34.5 ± 4.8^(b) pretreatment

Apo-2 ligand induced significant apoptosis in unstimulated B cells, in Bcells activated by LPS and in T cells activated. with PMA and ionomycin.It was previously reported that peripheral T cells can be predisposed toapoptosis by culturing the cells in the presence of IL-2 [Lenardo etal., Nature, 353:858-861 (1991)]. The present study showed thatpretreatment with IL-2 did sensitize the peripheral T cells to Apo-2ligand-induced death.

Example 7

Inhibition Assav Using Fas/Apo-1 and TNF Receptors

An assay was conducted to determine if the Fas/Apo-1 receptor, as wellas the type 1 and type 2 TNF receptors (TNF-R1 and TNF-R2), are involvedin mediating the apoptotic activity of Apo-2 ligand by testing ifsoluble forms of these receptors are capable of inhibiting the apoptoticactivity of purified, soluble Apo-2 ligand (described in Example 3).

9D cells were incubated (5×10⁴ cells/well) for 24 hours with a mediacontrol or Apo-2 ligand (0.3 μg/ml, prepared as described in Example 3)in the presence of buffer control, CD4-IgG control (25 μg/ml), solubleApo-1-IgG (25 μg/ml), soluble TNFR1-IgG (25 pg/ml) or soluble TNFR2-IgGfusion protein (25 μg/ml). Soluble derivatives of the Fas/Apo-1, TNF-R1and TNF-R2 receptors were produced as IgG fusion proteins as describedin Ashkenazi et al., Methods, 8:104-115° (1995). CD4-IgG was produced asan IgG fusion protein as described in Byrn et al., Nature, 344:667-670(1990) and used as a control.

As shown in FIG. 3C, none of the receptor-fusion molecules inhibitedApo-2 ligand apoptotic activity on the 9D cells. These results indicatethat Apo-2 ligand apoptotic activity is independent of Fas/Apo-1 and ofTNF-R1 and TNF-R2.

Example 8

Expression of Apo-2 Ligand mRNA in Mammalian Tissues

Expression of Apo-2 ligand mRNA in human tissues was examined byNorthern blot analysis (FIG. 4). Human RNA blots were hybridized to a³²P-labeled DNA probe based on the full-length Apo-2 ligand cDNA, or toa ³²P-labeled RNA probe based on the GenBank EST sequence, HHEA47M (seeExample 1). Human fetal RNA blot MTN (Clontech) and human adult RNA blotMTN-II (Clontech) were incubated with the DNA probe, while human adultRNA blot MTN-I (Clontech) was incubated with the RNA probe. Blots wereincubated with the probes in hybridization buffer (5×SSPE; 2 XDenhardt's solution; 100 mg/mL denatured sheared salmon sperm DNA; 50%formamide; 2% SDS) for 16 hours at 42° C. The blots were washed severaltimes in 1 X SSPE; 2% SDS for 1 hour at 65° C. and 50% freshly deionizedformamide; 1 ×SSPE; 0.2% SDS for 30 minutes at 65° C. The blots weredeveloped after overnight exposure, using a phosphorimager (Fuji).

The results are shown in FIG. 4. In fetal human tissues, Apo-2 ligandmRNA expression was detected in lung, liver and kidney, but not in braintissue. In adult human tissues, Apo-2 ligand mRNA expression wasdetected in spleen, thymus, prostate, ovary, small intestine, peripheralblood lymphocytes, heart, placenta, lung, and kidney. Little or noexpression was detected in testis, brain, skeletal muscle, and pancreas.The expression profile observed for Apo-2 ligand, as described above, isnot identical to that of Apo-1 ligand, which is expressed primarily in Tcells and testis [Nagata et al., supra].

Deposit of Material

The following cell line has been deposited with the American TypeCulture Collection, 12301 Parklawn Drive, Md. USA (ATCC):

Cell line ATCC Dep. No. Deposit Date 2935-pRK5-hApo-2L- CRL-12014 Jan.3, 1996 myc clone 2.1

This deposit was made under the provisions of the Budapest Treaty on theInternational Recognition of the Deposit of Microorganisms for thePurpose of Patent Procedure and the Regulations thereunder (BudapestTreaty). This assures maintenance of,a viable culture of the deposit for30 years from the date of deposit. The deposit will be made available byATCC under the terms of the Budapest Treaty, and subject to an agreementbetween Genentech, Inc. and ATCC, which assures permanent andunrestricted availability of the progeny of the culture of the depositto the public upon issuance of the pertinent U.S. patent or upon layingopen to the public of any U.S. or foreign patent application, whichevercomes first, and assures availability of the progeny to one determinedby the U.S. Commissioner of Patents and Trademarks to be entitledthereto according to 35 USC §122 and the Commissioner's rules pursuantthereto (including 37 CFR §1.14 with particular reference to 886 OG638).

The assignee of the present application has agreed that if a culture ofthe cell line on deposit should die or be lost or destroyed whencultivated under suitable conditions, the cell line will be promptlyreplaced on notification with another of the same plasmid. Availabilityof the deposited cell line is not to be construed as a license topractice the invention in contravention of the rights granted under theauthority of any government in accordance with its patent laws.

The foregoing written specification is considered to be sufficient toenable one skilled in the art to practice the invention. The presentinvention is not to be limited in scope by the construct deposited,since the deposited embodiment is intended as a single illustration ofcertain aspects of the invention and any constructs that arefunctionally equivalent are within the scope of this invention. Thedeposit of material herein does not constitute an admission that thewritten description herein contained is inadequate to enable thepractice of any aspect of the invention, including the best modethereof, nor is it to be construed as limiting the scope of the claimsto the specific illustrations that it represents. Indeed, variousmodifications of the invention in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description and fall within the scope of the appended claims.

1. Isolated biologically active human Apo-2 ligand comprising amino acidresidues 114-281 of FIG. 1A.
 2. The Apo-2 ligand of claim 1 comprisingamino acid residues 41-281 of FIG. 1A.
 3. The Apo-2 ligand of claim 2comprising amino acid residues 15-281 of FIG. 1A.
 4. The Apo-2 ligand ofclaim 3 comprising amino acid residues 1-281 of FIG. 1A.
 5. Isolatedbiologically active human Apo-2 ligand having amino acid residues 1-281of FIG. 1A.
 6. Isolated biologically active Apo-2 ligand having at leastabout 80% sequence identity with either of: (a) the full-length nativehuman Apo-2 ligand comprising amino acid residues 1-281 of FIG. 1A; (b)the extracellular region of native human Apo-2 ligand comprising aminoacid residues 41-281 of FIG. 1A; or (c) the extracellular region ofnative human Apo-2 ligand comprising amino acid residues 114-281 of FIG.1A.
 7. The Apo-2 ligand of claim 6 wherein said ligand has at leastabout 90% sequence identity with either of (a), (b), or (c).
 8. TheApo-2 ligand of claim 7 wherein said ligand has at least about 95%sequence identity with either of (a), (b), or (c).
 9. A chimericpolypeptide comprising the Apo-2 ligand of claim 1 fused to aheterologous polypeptide sequence.
 10. The chimeric polypeptide of claim9 wherein said heterologous polypeptide sequence is a tag polypeptidesequence.
 11. An antibody which binds to Apo-2 ligand.
 12. The antibodyof claim 11 wherein said antibody is a monoclonal antibody.
 13. Isolatednucleic acid encoding Apo-2 ligand.
 14. The nucleic acid, of claim 13wherein said nucleic acid encodes the Apo-2 ligand of claim
 1. 15. Thenucleic acid of claim 13 wherein said nucleic acid encodes the Apo-2ligand of claim
 2. 16. The nucleic acid of claim 13 wherein said nucleicacid encodes the Apo-2 ligand of claim
 5. 17. A vector comprising thenucleic acid of claim
 13. 18. A host cell comprising the vector of claim17.
 19. A method of producing Apo-2 ligand comprising culturing the hostcell of claim 18 and recovering the Apo-2 ligand from the host cellculture.
 20. A composition comprising Apo-2 ligand and apharmaceutically-acceptable carrier.
 21. The composition of claim 20wherein said Apo-2 ligand comprises the Apo-2 ligand of claim
 1. 22. Apharmaceutical composition useful for stimulating mammalian cellapoptosis comprising an effective amount of Apo-2 ligand in apharmaceutically-acceptable carrier.
 23. A method of inducing apoptosisin mammalian cells comprising exposing mammalian cells to an effectiveamount of Apo-2 ligand.
 24. A method of treating a mammal having cancer,comprising administering to a mammal diagnosed as having cancer aneffective amount of Apo-2 ligand.
 25. The method of claim 24 wherein theApo-2 ligand is administered to the mammal in combination with one ormore other therapies.
 26. The method of claim 25 wherein said one ormore other therapies are selected from the group consisting of radiationtherapy, chemotherapy, TNF-α, TNF-β, CD30 ligand, 4-1BB ligand, andApo-1 ligand.
 27. The method of claim 24 wherein said cancer is breastcancer, prostate cancer or ovarian cancer.
 28. An article ofmanufacture, comprising: a container; a label on said container; and acomposition contained within said container; wherein the compositionincludes an active agent effective for inducing apoptosis, the label onsaid container indicates that the composition can be used to induceapoptosis, and the active agent in said composition comprises Apo-2ligand.
 29. The article of manufacture of claim 28 further comprisinginstructions for administering the Apo-2 ligand to a mammal.